LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


DUST  PREVENTIVES 


AND 


ROAD  BINDERS 


BY 

PREVOST    HUBBARD 

ASSISTANT    CHEMIST,    OFFICE   OF   PUBLIC    ROADS,    U.   S.  DEPARTMENT   OF 

AGRICULTURE  ;    SECRETARY   OF   THE   COMMITTEE   ON 

ROAD    MATERIALS,    AMERICAN    SOCIETY 

FOR  TESTING    MATERIALS 


FIRST  EDITION 

FIRST    THOUSAND 


^ 

UMVERS'TY 


NEW   YORK 

JOHN    WILEY    &    SONS 

LONDON:   CHAPMAN  &  HALL,    LIMITED 

IQIO 


COPYRIGHT,  1910, 

BY 

PREVOST    HUBBARD 


Stanbopc  ipresft 

F.    H.   G1LSON     COMPANY 
•  BOSTON.     U.S.A. 


PREFACE 


THE  object  of  this  book  is  primarily  to  furnish  road  engineers 
with  a  working  knowledge  of  the  characteristic  properties  of  dust 
preventives  and  road  binders  now  in  use,  and  to  develop  certain 
fundamental  principles  relative  to  their  selection  and  application. 
During  the  past  few  years  there  has  been  a  rapidly  growing  de- 
mand for  such  information,  which  has  so  far  been  met  in  a  not 
altogether  satisfactory  manner.  The  subject  of  dust  prevention 
and  road  preservation  is  at  present  in  a  transitional  state,  and 
there  is  unquestionably  much  yet  to  be  learned  regarding  the  effect 
of  certain  properties  of  road  binders  upon  the  results  obtained  in 
practice.  It  is  hoped,  however,  that  this  work  may  serve  as  a  basis 
for  further  development  and  that  it  will  prove  of  some  assistance 
to  those  who  are  interested  in  the  use  of  such  materials. 

The  conclusions  as  presented  are  based  upon  experience  which 
the  author  has  acquired  both  in  the  laboratory  and  in  the  field  in 
the  past  five  years  of  his  service  with  the  United  States  Office 
of  Public  Roads.  During  his  connection  with  this  office  he  has 
had  under  his  personal  supervision  the  examination  of  practi- 
cally all  varieties  of  road  binders  and  their  use  under  varying 
conditions  in  many  parts  of  the  United  States. 

Throughout  this  book  the  mention  of  trade  names  as  applied 
to  the  results  of  examination  of  road  binders  has  for  the  most  part 
been  purposely  avoided  for  the  reason  that  different  lots  of  these 
products  have  not  as  a  rule  shown  definite  and  uniform  character- 
istics. The  ideas  of  producers,  with  reference  to  the  manufacture 
of  their  materials,  are  undergoing  a  process  of  evolution,  and  in 
spite  of  the  present  lack  of  uniformity  it  must  be  admitted  that 
a  general  tendency  is  being  exhibited  toward  the  improvement 
of  these  materials. 


206173 


VI  PREFACE 

The  author  here  wishes  to  express  his  indebtedness  to  Mr.  L. 
W.  Page,  Dr.  A.  S.  Cushman  and  Mr.  C.  S.  Reeve  for  their  kind 
assistance  and  advice  in  the  preparation  of  this  book,  and  also 
to  those  authors,  hereafter  referred  to,  from  whose  works  he  has 
quoted. 

PREVOST  HUBBARD. 

WASHINGTON,  D.  C.,  February  i,  1910. 


TABLE    OF    CONTENTS 


Chapter  Page 

I.  DUST  PREVENTION  AND  ROAD  PRESERVATION i 

II.   CLASSIFICATION  OF  DUST  PREVENTIVES  AND  ROAD  BINDERS 27 

III.  INORGANIC  DUST  PREVENTIVES  AND  ROAD  BINDERS 39 

IV.  INORGANIC  DUST  PREVENTIVES  AND  ROAD  BINDERS  (continued) ....  72 
V.  ORGANIC  NON-BITUMINOUS  DUST  PREVENTIVES  AND  ROAD  BINDERS  103 

VI.  HYDROCARBONS 112 

VII.  BITUMENS  EMPLOYED  AS  DUST  PREVENTIVES  AND  ROAD  BINDERS..  131 

VIII.  PETROLEUM  AND  PETROLEUM  PRODUCTS 143 

IX.  SEMI-SOLID  AND  SOLID  NATIVE  BITUMENS 178 

X.  APPLICATION  OF  PETROLEUM  AND  ASPHALTIC  MATERIALS 198 

XL  TARS  AND  TAR  PRODUCTS 229 

XII.  THE  APPLICATION  OF  TAR  AND  CONSTRUCTION  OF  BITUMINOUS  MAC- 
ADAM    275 

XIII.  THE  EXAMINATION  OF  BITUMINOUS  ROAD  MATERIALS  AND  INTER- 

PRETATION OF  RESULTS 324 

XIV.  METHODS  OF  TESTING  BITUMINOUS  ROAD  MATERIALS  PROPOSED  OR 

ADOPTED  BY  AMERICAN  SOCIETIES 373 

XV.  SELECTION  OF  DUST  PREVENTIVES  AND  ROAD  BINDERS 384 

APPENDIX 400 


vii 


DUST   PREVENTIVES   AND 
ROAD   BINDERS 

CHAPTER   I. 
DUST  PREVENTION  AND  ROAD   PRESERVATION. 

Introduction.  —  The  prevention  or  suppression  of  road  dust 
and  the  preservation  of  roads  are  undoubtedly  two  of  the  most 
important  problems  which  to-day  confront  road  engineers.  Pub- 
lic attention  in  these  matters  has  been  aroused  to  such  an  extent 
that  a  demand  for  less  dusty  and  more  lasting  roads  than  those  of 
the  past  is  becoming  more  insistent  every  day.  In  October, 
1908,  an  International  Road  Congress  met  at  Paris  mainly  for  the 
purpose  of  considering  these  two  problems.  From  the  mass  of 
data  contained  in  the  proceedings  of  this  Congress  one  important 
fact  stands  prominently  forth,  that  the  solution  of  these  problems 
lies  in  the  treatment  of  both  old  and  new  roads  with  chemical 
substances.  For  confirmation  of  this  fact  one  has  only  to 
consider  the  rapid  growth  of  the  chemical  road  preparation 
industries  both  in  numbers  and  in  importance  during  the  past 
four  years. 

While  the  purpose  of  this  book  is  to  treat  of  chemical  road 
materials,  a  proper  understanding  of  the  value  and  practical 
use  of  such  substances  cannot  be  attained  without  a  thorough 
knowledge  of  the  causes  and  effects  of  road  dust  formation  and 
road  deterioration,  and  the  relations  existing  between  them. 

This  chapter  will,  therefore,  deal  with  the  various  phases  of 
these  two  most  important  road  problems  and  in  later  chapters 
their  close  relation  to  the  subject  of  dust  preventives  and  road 
binders  will  be  developed. 


2  DUST   PREVENTIVES   AND    ROAD   BINDERS 

The  Dust  Problem.  —  It  has  been  said  that  nine-tenths  of  the 
dust  produced  by  man  originates  on  his  roads  and  streets.  While 
this  is  a  difficult  matter  to  estimate  with  any  degree  of  accuracy, 
it  is  nevertheless  true  that  a  large  proportion  of  dust  produced 
by  man  undoubtedly  comes  from  this  source,  and  equally  true 
that  far  more  havoc  is  wrought  by  road  dust  than  is  generally 
realized.  The  formation  of  road  dust  in  excessive  quantity  has 
given  rise  to  what  has  been  termed  in  recent  years  the  dust 
nuisance,  and  many  articles  have  appeared  in  the  press  from  time 
to  time  calling  attention  to  this  matter.  The  subject  has,  to  a 
great  extent,  been  discussed  from  individual  standpoints  and 
presented  to  the  reading  public  in  fragmentary  form,  and  while 
these  articles  have  undoubtedly  awakened  some  interest,  the 
attitude  taken  in  regard  to  its  importance  is  far  from  being  what 
it  should.  It  is  not  only  as  a  public  nuisance  that  dust  should 
be  considered,  but  as  a  public  menace  which  is  striking  directly 
at  the  life  of  many  individuals  and  in  various  insidious  ways  is 
lessening  public  comfort  and  public  health.  Much  money,  both 
public  and  private,  has  been  spent  in  attempts  to  remedy  the 
damages  caused  by  dust,  a  part  of  which  might  better  have  been 
used  in  curing  the  cause  rather  than  the  result. 

Since  the  memorable  work  of  Pasteur  upon  the  origin  of  cer- 
tain microscopic  organisms,  thousands  of  scientists  have  studied 
the  characteristics  and  habits  of  these  active  mites  of  the  in- 
visible world  which  surrounds  us.  As  early  as  1876,  Tyndall,  in 
a  discourse  upon  Fermentation  delivered  before  the  Glasgow 
Science  Lectures  Association,  showed  the  distribution  of  these 
organisms  to  be  closely  associated  with  the  transportation  of 
dust,  and  subsequent  study  has  proved  only  more  conclusively 
the  truth  of  his  assertions.  It  is  now  a  well- recognized  fact  that 
in  dustless  air  these  organisms  do  not  exist,  while  under  otherwise 
similar  conditions  they  are  found  in  increasing  numbers  as  the 
amount  of  dust  in  the  air  is  increased.  When  previously  steri- 
lized, milk  will  not  sour  in  dustless  air  no  matter  how  warm  it 
may  be,  meat  will  not  putrefy,  and  likewise  germ  diseases  cannot 
be  contracted  from  this  source.  In  dusty  air,  however,  the 


DUST   PREVENTION   AND    ROAD    PRESERVATION  3 

bacteria  of  milk  fermentation  and  of  meat  putrefaction  will, 
under  favorable  conditions,  quickly  spoil  the  milk  and  meat,  while 
the  presence  of  countless  other  germs  increases  to  a  great  extent 
the  probabilities  in  mankind  of  contracting  various  forms  of 
disease.  These  germs  readily  attach  themselves  to  dust  particles 
and  the  slightest  current  of  air  then  distributes  them  throughout 
the  atmosphere  where  their  war  upon  mankind  is  waged.  Among 
the  many  diseases  contracted  from  breathing  dust  laden  air  men- 
tion of  but  one,  tuberculosis,  should  be  sufficient  to  interest  every 
intelligent  reader  in  the  problem  of  dust  suppression.  When  the 
true  effect  of  dust  upon  public  health  is  fully  realized,  the  state- 
ment of  Tyndall  "  that  all  the  havoc  of  war,  ten  times  multiplied, 
would  be  evanescent  if  compared  with  the  ravages  due  to  atmos- 
pheric dust,"  can  well  be  believed. 

The  effect  of  road  dust  upon  some  classes  of  live  stock  is  also 
most  severe,  cattle  and  horses  in  particular  being  susceptible  to 
the  germs  of  tuberculosis  which  it  carries.  In  certain  districts 
devoted  to  the  raising  of  horses  it  has  been  noticed  by  breeders 
that  since  the  advent  of  the  fast  moving  motor  car,  with  its  great 
dust  raising  propensities,  this  disease  has  been  much  more  prev- 
alent among  their  stock  than  in  the  days  when  excessive  road 
dust  formation  and  its  aerial  transportation  was  of  less  common 
occurrence. 

The  personal  discomforts  to  which  those  using  and  living  near 
dusty  roads  are  subjected  are  too  well  known  to  need  discussion. 
Clothing  and  household  furnishings  are  damaged,  while  yards 
and  verandas  are  aften  made  untenantable.  For  these  reasons 
alone  real  estate  in  certain  localities  has  depreciated  in  value  to 
a  considerable  extent  within  the  last  few  years,  it  being  a  difficult 
matter  to  find  tenants  willing  to  put  up  with  the  annoyances  and 
inconveniences  resulting  from  the  road  dust. 

Its  effect  in  large  quantities  upon  vegetation  is  disastrous  in 
the  extreme  and  in  many  fruit  growing  districts  such  loss  has 
resulted  from  this  source  that  no  attempt  is  now  made  to  raise 
fruit  near,  dusty  roads.  The  distribution  of  road  dust  over  plants 
and  shrubbery,  besides  making  them  unsightly,  clogs  the  breath- 


4  DUST   PREVENTIVES   AND   ROAD   BINDERS 

ing  pores  of  the  leaves,  retards  their  growth,  and  in  some  instances 
has  been  known  to  kill  large  trees. 

While  some  classes  of  roads  and  pavements  are  benefited  by 
the  removal  of  dust,  others  are  greatly  damaged  by  this  means. 
The  macadam  is  a  good  example  of  the  latter  class,  one  of  the 
fundamental  principles  of  this  form  of  construction  being  that 
the  life  of  the  road  is  dependent  upon  the  retention  of  the  fine 
products  of  wear  which  serve  to  bind  together  and  hold  in 
place  the  coarser  fragments  of  stone  constituting  the  wearing 
surface.  Both  of  these  facts  at  once  connect  the  dust  problem 
with  that  of  road  preservation.  Before  taking  up  these  rela- 
tions in  detail,  however,  it  may  be  well  to  briefly  consider  the 
more  important  causes  of  dust  formation  on  roads. 

Causes  of  Dust  Formation  on  Roads. —  Broadly  speaking,  dust 
is  matter  in  a  finely  divided  state  produced  by  the  application 
of  energy  upon  matter  in  a  compact  state.  The  result  of  this 
energy  is  usually  termed  wear.  Dust  may  therefore  be  consid- 
ered as  the  product  of  wear,  and  wear  as  the  fundamental  cause 
of  dust  formation.  Other  factors  which  tend  to  remove  and  dis- 
tribute dust  when  formed,  thus  exposing  fresh  surfaces  to  wear, 
should,  however,  be  considered  in  this  connection.  All  forces 
which  tend  to  disintegrate  or  destroy  roads  will  of  necessity 
produce  wear  and  these  forces  may  be  conveniently  divided 
under  three  heads,  chemical,  physical  and  mechanical. 

In  regard  to  chemical  agencies,  it  has  long  been  known  that 
water  carrying  small  amounts  of  carbonic,  humus,  and  other 
acids  is  capable  of  slowly  decomposing  many  minerals  found  in 
the  rocks  commonly  used  for  road  building,  and,  as  it  is  mainly 
the  treatment  of  stone  roads  which  will  be  considered  in  this 
book,  a  brief  review  of  the  character  of  the  reactions  involved 
may  not  be  out  of  place  at  this  point.  Besides  these  weak 
acids  it  has  been  found  that  water  alone  is  capable  of  acting 
chemically  upon  many  rock  constituents,  causing  the  breaking 
down  into  secondary  products  of  the  primary  minerals,  espe- 
cially. While  it  is  true  that  this  action  is  at  first  very  slight, 
it  proceeds  at  a  more  rapid  rate  as  the  road  material  becomes 


DUST   PREVENTION   AND    ROAD    PRESERVATION  5 

finer,  and,  as  it  is  almost  constant,  in  the  end  produces  consid- 
erable effect.  Thus  the  feldspars,  which  are  of  very  common 
occurrence  in  road  materials,  are  partly  broken  down  into  kaolin 
or  other  secondary  products  with  the  solution  and  partial  removal 
of  the  soluble  material  also  formed.  While  this  action  tends  to 
disintegrate  the  rock,  it,  like  many  of  the  other  causes  of  wear, 
often  exerts  a  somewhat  beneficial  effect  upon  the  road,  the 
secondary  products  in  certain  cases  being  of  a  colloid  or  glue- 
like  character,  and  therefore  capable  of  binding  the  fragments 
of  undecomposed  material  together.  A  detailed  study  of  these 
reactions  will  be  found  in  publications  of  the  Department  of 
Agriculture,  by  Page,  Cushman  and  Hubbard  on  *  "  The  Cement- 
ing Power  of  Road  Materials  "  t  "The  Effect  of  Water  on  Rock 
Powders"  and  {  "The  Decomposition  of  the  Feldspars."  An- 
other way  in  which  the  chemical  action  of  water  sometimes 
acts  to  advantage  in  consolidating  a  road  surface  is  in  the  for- 
mation, through  solution  and  evaporation,  of  crystal  bodies 
such  as  calcite  which,  upon  crystallization,  forms  a  more  or  less 
rigid  bond.  In  some  instances,  a  combination  of  these  reac- 
tions takes  place  with  the  formation  of  both  colloid  and  crys- 
talloid bodies  which  interlock  and  produce  a  sort  of  set  similar 
to  that  which  takes  place  in  Portland  cement.  The  action  of 
water  upon  certain  slags  presents  a  good  example  of  this  kind 
of  reaction. 

The  most  important  physical  agencies  which  tend  to  hasten 
wear  and  therefore  the  formation  of  dust  are  (i)  the  disrupting 
effect  of  frost,  (2)  the  attrition  of  falling  rain,  (3)  the  trans- 
porting power  of  water,  and  (4)  the  action  of  wind.  The  effects 
of  frost  and  wind  are  of  course  much  more  important  than  the 
effects  of  rain  and  running  water,  and  have  to  be  considered  in 
particular  when  treating  a  road  with  reference  to  dust  preven- 
tion. It  may  be  added  that  in  selecting  a  material  which  shall 
act  as  a  permanent  dust  preventive,  care  should  be  taken  to 

*  U.  S.  Dept.  of  Agric.  Bureau  of  Chemistry  Bull.  85. 
f  U.  S.  Dept.  of  Agric.  Bureau  of  Chemistry  Bull.  92. 
J  U.  S.  Dept.  of  Agric.  Office  of  Public  Roads  Bull.  28. 


6  DUST  PREVENTIVES   AND    ROAD   BINDERS 

obtain  one  which  will  make  the  surface  as  nearly  waterproof  as 
possible,  especially  in  localities  where  the  winters  are  long  and 
severe. 

The  action  of  wind  has  an  important  bearing  upon  the  pre- 
vention of  dust,  although  it  has  a  somewhat  indirect  relation 
to  dust  formation.  If  all  of  the  products  of  wear  were  retained 
on  the  road  surface,  or  if  these  products  were  removed  in  a 
manner  similar  to  that  caused  by  running  water,  we  should 
experience  but  little  difficulty  with  our  roads.  The  removal  of 
fine  material  without  doubt  hastens  wear  by  exposing  surfaces 
which  would  otherwise  be  protected  by  a  cushion  of  the  products 
already  formed,  but,  if  these  products  were  not  susceptible 
to  the  action  of  wind,  there  would  be  no  dust  problem.  The 
action  of  wind,  therefore,  can  be  considered  as  one  of  the  most 
direct  causes  of  the  dust  nuisance. 

The  mechanical  agencies  are  abrasion,  impact,  local  com- 
pression and  shear.  All  of  these  forces  are  in  a  great  measure 
due  to  traffic;  abrasion  to  the  grind  of  steel-tired  wheels,  impact 
to  the  action  of  horses '  hoofs,  local  compression  to  heavily  loaded 
narrow  tired  wheels,  and  shear  to  the  tractive  force  exerted 
upon  the  road  surface  by  the  wheels  connected  with  the  driv- 
ing mechanism  of  self-propelled  vehicles.  In  respect  to  the  first 
two,  abrasion  and  impact,  considerable  judgment  can  be  exer- 
cised by  the  road  builder  as  to  the  selection  of  materials 
which  will  best  withstand  these  forms  of  attack.  For  this 
purpose  certain  physical  tests,  with  which  most  road  engineers 
are  familiar,  are  employed  in  order  to  determine  the  compar- 
ative value  of  different  rocks  with  respect  to  their  hardness, 
toughness,  and  resistance  to  wear.  Descriptions  of  these  tests 
will  be  found  in  most  textbooks  dealing  with  the  construction 
of  macadam  roads  and  need  not  here  be  considered  in  detail. 
By  making  use  of  such  tests  the  road  engineer  can,  to  a  great 
extent,  foretell  the  wearing  properties  and  other  characteristics 
of  any  road  stone  which  he  wishes  to  employ,  and,  as  will  be 
shown  later,  a  knowledge  of  these  properties  will  prove  of 
considerable  value  in  enabling  him  to  select  a  proper  dust 


DUST   PREVENTION   AND    ROAD    PRESERVATION  / 

preventive  or  binder  for  use  with  the  particular  kind  of  rock 
of  which  the  road  has  been  or  is  to  be  constructed. 

One  other  cause  or  source  of  dust  on  roads  is  the  transporta- 
tion or  deposition  of  extraneous  material  which  may  previously 
exist  as  dust  or  which,  under  the  action  of  the  forces  described 
above,  is  converted  into  dust  upon  the  road  surface.  This  is  a 
phase  of  the  problem  commonly  encountered  in  thickly  settled 
districts  and  often  requires  quite  different  treatment  from  the 
others  which  have  been  mentioned.  This  point  will  be  treated 
in  detail  in  a  later  chapter. 

Relation  of  the  Dust  Problem  to  That  of  Road  Preservation. — 
Upon  reviewing  the  causes  of  dust  formation  it  is  clearly  apparent 
that  most  of  them  have  a  direct  bearing  upon  road  deterioration, 
and  that  the  problem  of  dust  prevention  is,  therefore,  closely 
associated  with  that  of  road  preservation.  While  this  has  come 
to  be  a  well-recognized  fact,  it  may  not  be  amiss  to  consider  their 
relation  as  applied  to  different  types  of  roads.  For  this  com- 
parison roads  may  be  classified  under  the  following  three  head- 
ings: (i)  earth  roads;  (2)  broken  stone  and  gravel  roads;  (3) 
pavements. 

Earth  roads  being  composed  entirely  of  finely  divided  ma- 
terial, it  is  evident  that  most  of  the  forces  which  produce  dust, 
and  therefore  wear,  will  exert  a  greater  destructive  effect  upon 
them  than  upon  the  other  types  of  roads.  Because  of  this  prop- 
erty they  are  also  apt  to  have  but  little  inherent  mechanical 
stability,  and  this  fact  should  never  be  lost  sight  of  when  attempt- 
ing to  prevent  deterioration  by  the  application  of  a  dust  pre- 
ventive or  road  binder.  Owing  to  their  high  absorptive  capacity, 
water  or  any  other  liquid  in  large  quantities  lowers  their  mechani- 
cal stability,  although  in  moderate  quantities  these  agents  may 
act  as  binders.  Frost  and  the  transporting  power  of  water  are 
the  most  important  physical  agencies  which  tend  to  cause  deterio- 
ration in  earth  roads,  and  local  compression  and  shear  the  most 
important  mechanical  forces. 

Broken  stone  and  gravel  roads  have  considerably  greater 
mechanical  stability  than  earth  roads,  and  when  properly 


8  DUST   PREVENTIVES   AND    ROAD    BINDERS 

constructed,  therefore,  suffer  less  from  all  but  one  of  the  causes 
of  deterioration  of  the  latter.  Macadam  roads  in  particular 
are  designed  to  withstand  the  rapid  destructive  effects  of  water, 
abrasion,  impact,  and  local  compression  and  in  fact  make  use  of 
these  forces  to  a  great  extent  in  self-repair.  They  are  not,  how- 
ever, capable  of  successfully  resisting  the  shearing  stresses  to 
which  they  are  subjected  by  motor  traffic,  and  this  fact  is  the 
fundamental  cause  which  has  aroused  such  a  widespread  interest 
in  the  problems  of  dust  prevention  and  road  preservation,  and 
which  bids  fair  to  revolutionize  the  ordinary  form  of  macadam 
construction. 

Pavements  have  the  greatest  mechanical  stability  of  any  of  the 
three  types  of  roads  mentioned,  owing  to  the  presence  of  a  more  or 
less  rigid  binding  material,  or  to  regularity  in  the  setting  of  their 
integral  parts.  They  are  the  most  resistant  to  all  of  the  forces 
which  produce  dust  and  deterioration  and  are  for  the  most  part 
fairly  satisfactory  in  this  respect,  although  they  slowly  succumb 
to  these  forces  unless  repaired.  The  formation  and  deposition 
of  dust  upon  their  surfaces  from  outside  sources,  however,  often 
accelerates  deterioration,  especially  in  the  case  of  bituminous 
pavements,  and  so  this  last  cause  of  dust  formation  is  shown  to 
be  closely  associated  with  the  problem  of  road  preservation,  as  are 
all  of  the  others.  The  evolution  of  the  city  pavement  from 
the  earth  road  has  been  a  partial  solution  of  both  the  problems 
of  road  preservation  and  dust  prevention,  and  teaches  a  lesson 
that  should  prove  of  great  value  in  the  further  consideration 
of  the  contents  of  this  book. 

Effect  of  Automobile  Traffic  on  Roads. —  It  has  come  to  be 
a  well-recognized  fact  that  the  automobile  is  the  most  potent 
factor  which  at  the  present  time  operates  to  produce  dust  and 
destroy  roads.  During  the  past  two  years  much  study  has  been 
devoted  to  determining  the  actual  cause  or  causes  of  the  damage 
produced  by  this  class  of  traffic,  and  a  number  of  interesting 
theories  have  been  advanced  concerning  them.  Perhaps  the 
most  noticeable  effect  produced  by  the  passage  of  an  automobile 
over  the  surface  of  a  road  is  its  dust  raising  propensity.  Another 


DUST   PREVENTION   AND    ROAD    PRESERVATION 


fact  that  is  apparent  to  the  most  casual  observer  is  that  upon  a 
given  road  this  property  is  proportional  to  the  speed  at  which 
the  machine  is  driven.  When  moving  at  a  moderate  rate  but 
little  dust  is  raised,  in  fact  no  more  than  would  be  produced  by 
other  classes  of  traffic.  As  the  speed  is  increased  to  fifteen  miles 
per  hour  and  over,  however,  the  dust  cloud  following  in  the  wake 
of  the  vehicle  is  seen  to  grow  larger  and  larger.  The  same  effect 
may  be  observed  from  the  passage  of  a  railroad  train  over  steel 
rails  if  the  route  lies  through  a  dusty  country.  This  is  caused 
by  the  formation  of  a  partial  vacuum  and  consequent  air  currents 
behind  the  rapidly  moving  body,  which  whirl  aloft  any  fine  ma- 
terial with  which  they  come  in  contact  and  eventually  scatter  it 
over  the  surrounding  country. 


FIG.  i.     Macadam  Surface  Stripped  of  Fine  Material  by  Automobile. 

It  has  been  claimed  that  a  similar  vacuum  effect  is  produced 
by  the  rapid  passage  of  pneumatic  tires  over  a  road  surface,  but 
this  would  appear  to  be  but  slight  in  comparison  to  that  pro- 
duced behind  the  body  of  the  car  itself. 


IO  DUST  PREVENTIVES   AND   ROAD   BINDERS 

An  examination  of  almost  any  old  macadam  road  which  has 
been  subjected  to  heavy  automobile  traffic  will  show  that  much 
more  damage  has  been  wrought  than  can  be  accounted  for  by  the 
removal  of  surface  dust  alone.  Large  fragments  of  rock  consti- 
tuting the  wearing  surface  and  even  the  lower  course  are  found 
to  be  displaced  and  in  some  instances  thrown  up  in  windrows 
running  longitudinally  with  the  road.  In  extreme  cases  the  whole 
surface  has  become  disintegrated  and  only  a  loose  mass  of  broken 
stone  marks  the  former  site  of  the  once  well-bonded  road.  This 
effect  is  well  illustrated  by  Fig.  i,  which  shows  a  macadam  road 
that  has  been  practically  destroyed  by  automobile  traffic. 

It  would  seem,  therefore,  that  some  forces  other  than  induced 
air  currents  are  responsible  for  this  damage.  Two  notable  re- 
ports dealing  particularly  with  this  phase  of  the  subject  were 
presented  at  the  First  International  Road  Congress  in  1908,  one 
by  L.  W.  Page,*  Director  of  the  United  States  Office  of  Public 
Roads,  and  the  other  by  M.  A.  Petot,t  Professor  of  the  Faculty 
of  Sciences  of  Lille.  The  conclusions  presented  in  both  of  these 
papers  were  quite  similar  and  undoubtedly  explain  the  chief 
cause  of  the  destructive  action  of  motor  traffic  on  road  surfaces. 

To  quote  from  the  former  —  "As  already  stated,  the  broken 
stone  road  has  been  developed  to  withstand  the  wear  of  iron- 
tired  horse  vehicles,  and  has  met  successfully  the  demands  of 
suburban  and  rural  traffic  until  the  advent  of  the  motor  vehicle. 
When  in  its  highest  state  of  perfection,  the  rock  from  which  such 
a  road  is  made  is  so  suited  to  the  volume  and  character  of  traffic 
which  passes  over  it,  that  the  amount  of  dust  worn  off  is  only 
sufficient  to  replace  that  removed  by  wind  and  rains.  .  .  . 
When  such  a  road  is  subjected  to  continuous  fast  motor  traffic, 
entirely  new  conditions  are  brought  about.  .  .  .  Beyond  a  doubt 
this  most  injurious  action  of  motor  traffic  is  the  great  tractive  or 
shearing  force  exerted  by  the  driving  wheels  of  these  cars.  The 
fine  dust  which  ordinarily  acts  as  a  cementing  agent  to  the  road 
surface  is  thrown  into  the  air  to  be  carried  off  by  the  wind,  or 

*  "The  Effect  of  Modern  Traffic  on  Broken  Stone  Roads." 

t  "EfJets  des  Nouveaux  Modes  de  Locomotion  sur  les  Chaussees." 


DUST   PREVENTION   AND   ROAD   PRESERVATION 


I  I 


that  remaining  on  the  road  is  so  loosened  that  it  is  easily  washed 
into  the  gutters  by  rain.  The  pneumatic  rubber  tire  wears  off 
from  the  broken  stone  of  the  road  little  or  no  dust  to  replace 
that  thus  removed,  and  the  result  is  that  the  stones  become 
loose  and  rounded,  giving  the  greatest  resistance  to  traction  and 
allowing  water  to  make  its  way  freely  to  the  foundation  of  the 
road.  ...  To  sum  this  matter  up  briefly,  the  pneumatic  tire, 
or  any  type  of  tire  which  propels  a  vehicle,  must  have  sufficient 
tractive  resistance  to  overcome  the  load  of  the  vehicle.  This, 
of  necessity,  must  cause  a  shear  on  the  road  surface  which  varies 
with  the  weight  and  speed  of  the  vehicle.  The  broken  stone  road 
surface  has  little  power  to  resist  a  shearing  stress,  consequently 
the  fine  material  of  which  it  is  composed  is  thrown  into  the 
air.  .  .  .  Aside  from  the  dust  carried  from  the  road  in  this  man- 
ner, this  shearing  force  of  the  motor  car  has  a  decided  disinte- 
grating effect  on  the  surface  of  the  road." 


FIG.  2.     Action  of  Fast  Moving  Motor  Car  upon  Road  Surface. 

(Speed  80  miles  per  hour) 

The  destructive  action  exerted  by  the  rear  wheels  of  a  motor 
car  moving  at  high  speed  is  very  plainly  shown  in  Fig.  2. 


12  DUST  PREVENTIVES  AND   ROAD   BINDERS 

While  the  vacuum  effect  and  direct  shearing  force  produced  by 
rapidly  moving  automobiles  are  the  most  important  causes  of 
dust  formation  and  road  deterioration,  mention  should  be  made 
of  the  side  slip  and  skidding  effect  of  the  tires,  especially  upon 
curves.  This  action,  while  somewhat  reduced  by  anti-skidding 
devices,  is  often  terribly  destructive  when  it  does  take  place, 
particularly  in  cases  where  armored  tires  are  used.  When  pro- 
nounced irregularities  occur  in  the  surface  of  roads  the  automobile 
is  also  apt  to  cause  considerable  damage,  for  a  small  hole  once 
started  grows  rapidly  under  its  action,  especially  in  wet  weather, 
owing  to  the  sloughing  effect  of  the  heavily  tired  wheels  which 
throw  the  accumulation  of  water  and  mud  out  of  these  holes  upon 
the  road  surface. 

The  amount  of  damage  which  the  automobile  has  already  done 
to  macadam  roads  can  best  be  demonstrated  by  a  glance  at 
official  reports  on  this  subject,  obtained  from  various  sources. 
Thus,  in  England,  seven  counties  near  London  report  that  the 
percentage  of  increase  of  cost  of  care  and  maintenance,  claimed 
to  be  due  to  the  use  of  the  automobile,  has  been  from  twenty- 
two  to  seventy-seven  per  cent.  Statistics  of  the  Massachusetts 
Highway  Commission  show  that  about  fifty-three  per  cent  of 
the  destruction  of  state  highways  is  due  to  automobiles,  and 
reports  of  a  similar  nature  have  been  made  by  French  engineers. 

Earth  roads,  having  less  mechanical  stability  than  any  other 
type  of  road,  are,  of  course,  greatly  damaged  by  the  automobile, 
and  dust  formation  is  invariably  excessive  on  such  roads  which 
are  subjected  to  even  a  moderate  amount  of  motor  car  traffic. 

It  is  only  upon  street  pavements  that  motor  vehicles  produce 
no  observable  deterioration.  In  fact  this  class  of  traffic  here 
seems  to  be  less  injurious  than  any  other,  owing  to  the  great 
resistance  offered  to  shearing  stresses  by  the  pavement  itself, 
and  to  the  protective  action  of  the  rubber  tires  which  reduces 
impact  and  abrasion  to  a  minimum.  Because  of  the  continued 
deposition  of  extraneous  material  upon  the  surface  of  the  pave- 
ment, however,  much  dust  is  often  produced  by  these  vehicles, 
so  that  even  here  the  problem  of  dust  prevention  exists.  The 


DUST  PREVENTION  AND   ROAD  PRESERVATION  13 

automobile  is,  therefore,  invariably  held  responsible  for  the  dust 
nuisance  if  not  for  road  deterioration. 

While,  as  has  been  shown,  the  automobile  is  undoubtedly  to 
blame  for  the  greater  part  of  both  troubles,  it  should  be  remem- 
bered that  the  dust  nuisance  on  a  somewhat  smaller  scale  existed 
long  before  its  advent.  If  it  has  resulted  in  an  awakened  interest 
in  this  problem  alone,  it  will  have  served  a  valuable  purpose,  but 
besides  this  it  has  exerted  a  beneficial  influence  in  arousing -the 
public  at  large  to  the  knowledge  that  good  roads  are  necessary 
to  the  welfare  of  any  community,  and  thus  has  been  instrumental 
in  the  construction  of  many  miles  of  road  which  would  otherwise 
have  remained  unbuilt.  Bad  roads  are  almost  as  injurious  to  the 
automobile  as  the  automobile  is  to  the  road  itself,  so  that  the 
development  of  a  practical  road  which  will  withstand  its  destruc- 
tive action  is  a  matter  for  cooperation  between  the  automobilist, 
the  road  engineer  and  the  general  public. 

Methods  of  Preventing  Dust  and  Preserving  Roads. —  Many 
methods  of  solving  the  problems  of  dust  prevention  and  road 
preservation  have  been  suggested  and  tried,  and  while  a  large 
proportion  have  in  themselves  proved  unsatisfactory,  much 
valuable  information  has  been  obtained.  There  is  probably  no 
one  solution  that  will  meet  all  cases  and  it  is  only  by  considering 
the  collective  results  of  those  who  have  experimented  along  these 
lines  that  a  proper  appreciation  of  the  great  number  of  factors 
which  bear  upon  the  subject  can  be  obtained. 

In  regard  to  the  dust, problem  alone  there  would  seem  to  be 
three  general  ways  in  which  it  might  be  solved:  (i)  by  the  sani- 
tary removal  of  dust  from  road  surfaces,  (2)  by  the  retention 
of  dust  on  the  road  surface,  and  (3)  by  the  prevention  of  dust 
formation. 

The  first  of  these  methods  is  usually  followed  in  the  case  of 
city  pavements  and  involves  sprinkling  the  street  with  water 
and  removing  the  moistened  dust  by  sweeping.  This  is  an 
expensive  procedure,  calling  for  almost  continuous  labor  and 
close  attention  and  is  clearly  impracticable  for  country  roads. 
While  it  is  a  most  useful  and  necessary  method  for  the  class  of 


14  DUST  PREVENTIVES  AND   ROAD   BINDERS 

pavements  found  in  cities  and  towns,  it  is  unsuited  for  roads 
which  are  either  composed  entirely  of  fine  material  or  are 
dependent  upon  the  retention  of  fine  material  upon  their  sur- 
faces. Even  for  pavements  the  method  as  outlined  above  can 
sometimes  be  modified  for  the  better,  as  will  be  shown  later. 

The  retention  of  dust  upon  road  surfaces  may  be  brought 
about  in  either  one  of  two  Ways  or  by  a  combination  of  both. 
The  first  lies  in  the  control  of  those  forces  which  tend  to  remove 
dust  and  the  second  by  treatment  of  the  surface  dust  with  a 
view  toward  making  it  less  susceptible  to  their  influences.  In 
regard  to  the  natural  forces  which  tend  to  remove  dust,  i.e., 
wind  and  running  water,  it  would  seem  that  natural  agencies 
might  in  many  instances  be  employed  to  counteract  them. 

It  is  a  well-known  fact  that  the  presence  of  trees  mitigates 
the  harshness  of  weather  conditions  in  their  immediate  vicinity. 
As  these  conditions  have  an  important  effect  upon  a  road,  it 
is  often  possible  by  the  proper  maintenance  of  trees  and  hedges 
along  a  roadside  to  prevent  much  of  the  dust  from  being  removed. 
Thus,  shade  trees  will  keep  a  road  for  a  considerable  time  in  a 
moist  or  semi-moist  condition  after  a  rainfall  and  materially 
aid  in  the  laying  of  dust.  At  the  same  time,  both  trees  and 
hedges  protect  a  road  from  the  full  sweep  of  winds  and  there- 
fore prevent,  to  some  extent,  the  removal  of  dust  by  this 
means.  Proper  sodding  and  care  of  embankments  along  a 
road  will  also  often  reduce  the  formation  of  dust,  by  prevent- 
ing the  mechanical  transportation  of  extraneous  fine  material 
to  the  road  surface,  and  retard  or  prevent  the  removal  of  much 
fine  material  by  running  water. 

With  respect  to  overcoming  the  dust  raising  effect  of  automo- 
biles, it  would  seem  that  regulations  restricting  the  speed  of 
such  vehicles  would,  if  enforced,  be  at  least  a  partial  solution  of 
the  problem,  as  the  amount  of  dust  raised  is  proportional  to 
the  speed  at  which  the  machine  is  driven.  The  demand  for 
rapid  transportation  has,  however,  become  so  general  that 
very  severe  restrictions  cannot  well  be  imposed,  although  exces- 
sive speeds  should  certainly  be  forbidden,  except  upon  roads 


DUST   PREVENTION   AND    ROAD   PRESERVATION  15 

especially  adapted  to  very  rapid  traffic.  In  some  instances, 
mainly  in  city  and  suburban  parks,  the  problem  has  been  met 
by  forbidding  the  passage  of  automobiles  over  the  roads,  but 
this  is  certainly  an  unsatisfactory  solution  of  the  difficulty  as  the 
automobile  is  not  only  a  thing  of  the  present  but  of  the  future 
as  well,  and  cannot  be  thus  easily  disposed  of. 

The  automobilist  himself  has  attempted  to  solve  the  dust 
problem  to  some  extent,  and  in  cooperation  with  the  automo- 
bile manufacturer  has  demonstrated  a  number  of  valuable  facts 
which,  however,  have  not  been  followed  up  to  the  best  advan- 
tage. During  the  summer  of  1907  the  Royal  Automobile  Club, 
of  England,  instituted  a  series  of  motor  dust  trials  with  a  view 
toward  finding,  if  possible,  some  method  of  overcoming  the 
dust  raising  tendency  of  motor  cars,  by  means  of  mechanical 
devices.  A  day  was  selected  for  observing  the  effect  of  the  vari- 
ous machines  traveling  over  a  dust  lain  track  with  just  sufficient 
breeze  to  move  the  dust  raised  by  each  car,  but  not  enough  to 
create  such  a  dust  cloud.  It  was  very  difficult  to  distinguish 
much  difference  in  the  character  of  the  dust  cloud  raised  by 
different  cars,  although  those  fitted  with  bodies  high  from  the 
ground  or  else  very  low  raised  less  dust  than  the  average. 
Several  novel  devices  were  tried  with  more  or  less  success. 
One  of  these  which  gave  fairly  good  results  was  a  machine  made 
with  a  body  high  from  the  ground  and  fitted  with  an  under 
shield  and  cased  wheels.  The  best  results. were  obtained  with 
a  car  carrying  a  flat  steel  bottom  under  body,  with  sides  over- 
lapping the  sides  of  the  car,  and  shoes  instead  of  mud  guards. 
The  under  screen  was  only  six  inches  from  the  ground,  and  pro- 
jected beyond  the  radiator  in  front  so  as  to  catch  the  deflected 
wind  from  the  face  of  the  car  and  pass  it  between  the  screen 
and  the  car  instead  of  between  the  car  and  the  road.  This 
car  raised  very  little  dust  at  a  speed  of  thirty  miles  per  hour. 

The  surface  treatment  of  roads  with  a  view  toward  making 
them  less  susceptible  to  dust  raising  forces  has  undoubtedly 
received  more  attention  than  any  other  one  method  of  over- 
coming the  dust  nuisance.  The  materials  employed  in  such 


1 6  DUST   PREVENTIVES   AND   ROAD  BINDERS 

treatment  are  known  as  dust  palliatives  and  will  be  fully  treated 
of  in  later  chapters.  For  the  present  it  will  be  sufficient  to  say 
that  they  are  for  the  most  part  temporary  binding  mediums 
which  moisten  and  hold  the  dust  particles  together  and  to  the 
surface  of  the  road.  Water  is  the  best  known  and  most  gene- 
rally used  material  for  this  purpose,  although  perhaps  the  least 
satisfactory  except  when  employed  immediately  before  the 
road  is  to  be  cleaned.  Numerous  chemical  substances  espe- 
cially manufactured  for  this  purpose,  as  well  as  chemical  by- 
products, have  also  been  used  with  more  or  less  success  accord- 
ing to  their  manner  of  application  and  the  local  conditions 
which  they  have  had  to  meet. 

The  retention  of  dust  upon  the  road  surface  by  any  of  the 
means  described  above  tends  in  a  measure  to  solve  the  problem 
of  road  preservation  by  forming  a  cushion  coat  which  protects 
the  underlying  road  from  wear,  and  in  the  case  of  broken  stone 
roads  acts  as  a  binder  for  the  coarser  fragments.  If,  however, 
too  much  dust  is  retained  by  the  road  a  disagreeable  surface 
condition  is  produced,  especially  in  wet  weather  when  the  dust 
becomes  mud.  This  fact  naturally  leads  to  a  consideration  of 
means  for  preventing  excessive  dust  formation,  which  is  the 
third  solution  of  the  dust  problem  as  outlined. 

Prevention  of  dust  formation  means,  according  to  our  defini- 
tion of  dust,  prevention  of  wear,  and  it  is  therefore  a  direct 
method  of  road  preservation.  Dust  from  outside  sources  will, 
however,  always  be  encountered  and  when  excessive  will  have 
to  be  dealt  with  according  to  one  or  more  of  the  methods  de- 
scribed under  the  first  two  headings.  That  is,  even  on  roads 
where  the  products  of  wear  are  reduced  to  a  mimimum  by 
measures  taken  to  prevent  dust  formation,  the  road  may  be- 
come dusty  from  outside  sources  and  this'  dust  should  either 
be  removed  or  retained  upon  the  road  surface  by  some  suitable 
means.  The  latter  method  is  seldom  advisable  except  when 
employed  merely  to  keep  down  the  dust  until  it  can  be  removed 
in  a  sanitary  manner. 

The  first  method  which  may  be  mentioned  of  preventing 


DUST   PREVENTION   AND    ROAD   PRESERVATION  I/ 

dust  formation  on  roads  is  the  use  of  wide  tires  or  rubber  tires 
on  horse  drawn  vehicles  in  place  of  the  ordinary  narrow  steel 
tire.  It  is  a  well-known  fact  that  the  narrow  steel  tire  under 
heavy  loads  cuts  into  the  less  resistant  types  of  roads,  forming 
deep  ruts  which  soon  fill  with  water  and  serve  as  starting  points 
for  excessive  wear,  even  by  rubber  tired  vehicles.  Regulations 
against  excessive  speed  of  motor  cars  undoubtedly  tend  to  pre- 
serve the  roads  from  their  destructive  action  as  well  as  to  pre- 
vent the  removal  of  dust,  as  the  damage  caused  by  such  machines 
increases  with  their  weight  and  speed.  The  use  of  chains  and 
other  metal  anti-skidding  devices  should  also  be  forbidden,  for 
practically  no  form  of  country  road  can  successfully  withstand 
their  wear  and  tear,  even  if  the  road  has  previously  been  treated 
with  a  dust  preventive  or  road  binder.  The  avoidance  of  sharp 
curves  in  laying  out  new  roads  will  also  be  an  aid  to  road  pres- 
ervation, as  the  greatest  damage  from  skidding  is  apparent  at 
such  places. 

One  solution  of  the  problem  which  has  been  seriously  consid- 
ered by  some  road  engineers  is  the  construction  of  special  auto- 
mobile highways  over  which  no  other  kind  of  traffic  shall  be 
allowed  to  pass.  This  would  in  many  cases  involve  the  con- 
struction of  double  highways,  one  side  being  reserved  for  horse 
drawn  and  the  other  for  self-propelled  vehicles.  While  such 
highways  might  have  many  desirable  features,  at  the  present 
time  their  construction  involves  too  great  an  expenditure  of 
money  to  be  generally  adopted.  Where  this  plan  has  been 
carried  out,  however,  the  results  have  proved  satisfactory. 

For  ordinary  macadam  roads  the  selection  of  a  hard  tough 
stone  for  the  body  of  the  road,  and  of  good  binding  screenings 
for  the  surface,  would  undoubtedly  improve  the  condition  of 
many,  but  even  the  best  of  such  roads  will  rapidly  succumb  to 
excessive  automobile  traffic.  When  only  the  softer  kind  of 
rocks  are  to  be  had,  certain  modifications  of  the  customary 
form  of  macadam  may  be  followed  to  advantage  in  increasing 
the  resistance  of  the  road  to  wear.  Thus  the  use  of  the  smaller 
sizes  of  crushed  stone  in  the  foundation  course  and  of  the  larger 


1 8  DUST   PREVENTIVES   AND   ROAD   BINDERS 

sizes  in  the  wearing  course  will  in  some  cases  prove  to  be  the 
best  practice.  To  quote  from  a  paper  on  this  subject  by  A.  N. 
Johnson:*  "The  fact  that  pieces  of  rock  from  two  to  three 
inches  in  size  will  lock  or  key  together  more  firmly  than  one- 
inch  size  makes  a  surface  composed  of  the  larger  sizes  resist 
more  effectively  the  action  of  automobile  traffic.  In  many 
instances  observed  by  the  writer  it  has  been  noticed  that  the 
first  place  to  give  way  has  been  where  there  evidently  has  been 
a  cluster  of  finer  particles."  When  employing  a  dust  preven- 
tive or  road  binder  with  stone  of  poor  wearing  quality  this 
form  of  construction  can  also  undoubtedly  be  employed  to  ad- 
vantage, with  certain  modifications  which  will  be  described  in 
another  place. 

The  construction  of  country  roads  similar  to  our  city  pave- 
ments would  undoubtedly  solve  the  problem  of  road  preserva- 
tion to  a  great  extent,  but  unfortunately  this  is  out  of  the  ques- 
tion at  the  present  time  on  account  of  cost.  By  approaching 
the  city  pavement  form  of  construction  as  close  as  economy 
will  permit,  however,  a  long  step  will  be  taken  in  the  right 
direction,  and  this  fact  will  be  appreciated  as  the  subject  of 
road  binders  is  developed. 

Careful  maintenance  is  always  a  most  necessary  adjunct  to 
preservation  even  of  the  most  resistant  forms  of  roads  and 
pavements.  This  fact  would  seem  to  be  so  axiomatic  as  to  hardly 
need  discussion  and  yet  in  this  country  in  particular  the  main- 
tenance of  roads  is  not  given  proper  attention,  and  is  often 
sadly  neglected.  This  is  not  so  often  the  fault  of  the  engineer 
as  of  the  people  or  controlling  bodies  who  have  to  do  with  the 
appropriation  of  road  funds.  Among  those  who  are  not  well 
informed  on  the  subject  the  prevalent  idea  seems  to  be  that  a 
road  once  well  built  should  last  indefinitely,  with  little  or  no 
attention,  except  perhaps  for  a  few  slight  repairs  now  and  then. 
As  a  matter  of  fact  this  is  far  from  being  the  case.  All  classes 
of  roads  and  pavements  require  almost  constant  attention  if 

*  Specifications  and  Notes  on  Macadam    Road  Construction,   Journal  Western 
Society  of  Engineers,  December,  1908. 


DUST   PREVENTION   AND    ROAD    PRESERVATION  19 

they  are  to  be  kept  in  first  class  condition,  and  the  expenditure 
of  money  for  this  purpose  proves  in  the  long  run  to  be  good 
economy.  The  European  nations  are  considerably  in  advance 
of  us  in  this  respect  and  the  sooner  we  follow  their  lead  the 
better.  This  point  cannot  be  urged  too  strongly  in  the  case  of 
roads  treated  with  bituminous  binders,  for  deterioration  in  the 
majority  of  such  roads  proceeds  at  a  rapid  rate  when  once 
begun. 

The  use  of  chemical  road  binders  in  the  construction  and 
maintenance  of  roads  seems  to  be  the  most  likely  method  of 
solving  the  problem  of  road  preservation,  and  many  experiments 
have  been  conducted  along  these  lines  by  road  engineers.  A 
great  number  of  materials  have  been  employed,  various  methods 
of  application  have  been  resorted  to,  and  results  of  the  most 
varied  and  seemingly  conflicting  character  have  been  obtained. 
Enough  has  been  accomplished,  however,  to  show  the  possibili- 
ties of  the  use  of  chemical  binders  and  the  road  engineer  has 
come  to  regard  them  as  his  salvation.  As  in  the  case  of  dust 
palliatives,  large  industries  have  been  developed  for  the  pur- 
pose of  supplying  road  binders  of  one  kind  or  another  and  both 
classes  of  materials  are  now  furnished  by  many  manufacturers. 
In  fact  the  differences  between  the  two  are,  as  will  be  shown 
later,  often  but  differences  in  concentration  of  the  same  kind  of 
binding  base  held  by  each. 

Road  binders  are  at  present  employed  in  two  general  ways: 
(i)  in  the  surface  treatment  of  roads  and  (2)  in  the  internal 
treatment  of  roads.  Their  primary  function  is  to  bind  the 
wearing  fragments  of  the  road  together  sufficiently  to  with- 
stand the  disrupting  strains  to  which  the  road  is  likely  to  be 
subjected.  They  should  also  waterproof  the  road  and  thus 
minimize  the  effects  of  water  and  frost.  A  good  road  binder 
thus  reduces  wear  and  also  dust  formation.  Some  produce  a 
rigid  bond  and  others  a  more  or  less  resilient  bond.  The  latter 
are  to  be  preferred  for  roads  subjected  to  heavy  horse  drawn 
traffic  as  they  lessen  the  effect  of  impact  from  the  horses'  shoes 
and  of  abrasion  from  steel  tired  wheels. 


2O  DUST   PREVENTIVES   AND   ROAD   BINDERS 

Road  binders  employed  in  the  surface  treatment  of  roads 
hold  an  intermediate  position  between  the  dust  palliatives  and 
the  heavy  internal  binders.  They  are  extensively  employed  in 
the  treatment  of  old  broken  stone  or  gravel  roads,  while  the 
latter  are  made  use  of  in  new  construction  work  and  in  the 
resurfacing  of  old  roads.  Both  the  dust  palliatives  and  road 
binders  will  be  classified  and  described  in  later  chapters  and 
need  not  be  further  considered  at  this  point,  other  than  to  state 
that  they  do  not  keep  a  road  dustless  for  any  great  length  of 
time,  although  they  may  reduce  the  formation  of  dust  from  the 
road  material  proper.  Where  dust  formation  from  other  sources 
is  excessive  the  two  classes  should  be  employed  conjunctively. 

Necessity  for  Specific  Information  Concerning  Dust  Preven- 
tives and  Road  Binders.  —  Owing  to  the  rapidity  with  which 
the  production  of  dust  preventives  and  road  binders  has  devel- 
oped and  the  great  number  of  preparations  now  on  the  market, 
as  well  as  to  the  discouraging  and  often  misleading  results  ob- 
tained by  their  experimental  use,  the  road  engineer  is  frequently 
at  a  loss  to  decide  upon  just  what  material  he  should  use  and 
just  how  he  should  afterwards  employ  it  to  best  advantage. 
The  information  which  he  has  had  to  rely  upon  is  for  the  most 
part  that  which  he  can  obtain  by  reading  reports  of  experiments 
which  in  many  cases  have  been  conducted  under  entirely  different 
conditions  from  those  with  which  he  has  to  contend,  or  else  from 
the  descriptive  circulars  issued  by  manufacturers  of  these  prep- 
arations. So  many  conflicting  opinions  are  held  by  different 
parties  who. claim  to  be  experts  on  the  subject  that  their  collec- 
tive ideas  serve  only  to  confuse  him  unless  he  has  the  time  and 
inclination  to  work  out  the  problem  for  himself  and  separate 
the  facts  from  the  fallacies.  To  do  this  requires  a  certain  amount 
of  chemical  knowledge,  in  which  he  is  usually  deficient,  never 
before  having  been  called  upon  to  combine  chemistry  with  road 
building.  While  it  is  true  that  the  development  of  the  paving 
industries  has  resulted  in  the  accumulation  of  much  data,  both  on 
the  chemical  and  mechanical  side  of  pavement  construction, 
which-  is  of  unquestioned  value  in  connection  with  modern  road 


DUST  PREVENTION  AND   ROAD   PRESERVATION  21 

work,  the  subjects^  of  dust  prevention  and  road  preservation 
require  somewhat  different  treatment.  In  other  words  the 
principles  which  have  been  established  in  the  paving  industry 
will  often  have  to  be  modified  and  differently  applied  in  consider- 
ing the  treatment  and  construction  of  roads  with  dust  preven- 
tives and  road  binders.  For  example,  the  expensive  paving 
materials  and  refinements  of  construction  in  building  and  main- 
taining city  pavements  cannot  usually  be  employed  in  road 
work  on  account  of  cost,  and  recourse  must,  therefore,  be  had 
to  cheaper  materials  and  cheaper  forms  of  construction  which 
would  not  be  considered  good  practice  in  the  former  case. 

It  is  evident,  therefore,  that  necessity  exists  for  specific  infor- 
mation relative  to  the  chemical  and  physical  characteristics  of 
dust  preventives  and  road  binders,  which  will  enable  the  road 
engineer  to  select  and  specify  materials  best  suited  to  his  needs, 
and  also  as  to  the  best  method  of  applying  such  materials.  The 
whole  subject  is  at  present  in  an  undeveloped  state  and  there  is 
much  yet  to  be  learned,  but  certain  fundamental  facts  have  been 
demonstrated  which,  if  generally  understood,  should  do  much 
toward  putting  matters  on  a  firm  footing  and  aid  in  clearing  up 
the  apparent  contradictions  which  now  exist.  While  the  road 
engineer  has  been  experimenting  with  various  materials  about 
which  he  knows  little  or  nothing  regarding  their  chemical  and 
physical  properties,  the  manufacturer  of  these  products  has  also 
been  experimenting  on  his  own  account  both  at  the  working 
expense  of  the  engineer  who  has  employed  his  material  and  at 
the  financial  expense  of  the  public.  As  the  subject  is  in  its 
infancy  this  is  of  course  only  a  natural  procedure  on  the  part 
of  any  progressive  manufacturer  who  wishes  to  improve  his  prod- 
uct, but  except  to  himself  it  has  resulted  in  much  confusion, 
owing  to  changes,  of  which  the  engineer  knows  nothing,  made  in 
products  whose  only  recognized  means  of  identification  are  their 
trade  names.  This  fact  has  more  than  once  come  under  the  ob- 
servation of  the  author  both  in  laboratory  and  field  work. 

Another  although  somewhat  similar  cause  of  confusion  lies 
in  the  great  variations  in  composition  of  certain  classes  of 


22  DUST   PREVENTIVES   AND    ROAD    BINDERS 

materials  known  under  very  general  names.  Thus  coal  tars 
vary  so  among  themselves  that  it  is  safe  to  say  that  no  two  tars 
obtained  from  different  localities  have  the  same  composition, 
and  in  fact  samples  obtained  from  the  same  plant  at  different 
times  will  often  show  considerable  variations  in  character. 

How  then,  it  may  be  asked,  can  the  road  engineer  even  iden- 
tify materials  which  he  has  employed  and  how  can  he  intelli- 
gently select  and  specify  those  materials  which  will  give  him 
the  best  results?  These  are  the  questions  that  would  seem  to 
be  of  paramount  importance  and  which  can  be  answered  only 
by  a  careful  review  and  digestion  of  all  the  reliable  data  to  be 
obtained  from  both  theory  and  practice.  Without  this  knowl- 
edge work  with  dust  preventives  and  road  binders  will  be  purely 
experimental  and  most  experiments  so  made  will  continue  to  be 
as  in  the  past  of  doubtful  value  both  to  the  experimenter  and 
those  who  should  profit  by  his  experiments. 

The  Future  Road.  —  In  connection  with  the  problem  of  road 
preservation  much  discussion  has  arisen  as  to  what  form  the 
future  road  will  take.  To  the  author's  mind  the  most  plausible 
answer  to  this  question  would  seem  to  be  some  form  of  city 
pavement,  probably  of  a  bituminous  nature.  This,  however, 
is  a  matter  of  the  far  distant  future  and  will  be  accomplished 
only  by  a  slow  evolution  of  the  modern  macadam  through  the 
stages  of  a  bituminous  treated  surface,  a  bituminous  bound 
wearing  course  with  ordinary  macadam  base,  and  a  bituminous 
bound  wearing  course  with  cement  concrete  base.  The  mac- 
adam is  at  present  passing  through  the  first  stage  and  while  the 
second  is  within  sight,  some  time  will  probably  elapse  before  it 
is  generally  adopted. 

In  connection  with  the  two  methods  mentioned  above  for 
treating  roads  with  chemical  road  binders,  i.e.,  surface  treat- 
ment and  internal  treatment,  there  are  two  problems  con- 
nected with  the  preservation  of  roads.  The  first  deals  with 
the  preservation  of  existing  roads  and  the  second  with  that  of 
new  roads  which  are  being  constructed.  Until  the  old  roads 
are  sufficiently  worn  to  require  resurfacing,  it  is  evident  that 


DUST   PREVENTION   AND   ROAD   PRESERVATION 


surface  treatment  is  the  most  economical.  In  resurfacing  or 
construction  work,  however,  internal  treatment  can  be  em- 
ployed to  advantage.  At  present  this  is  most  generally  accom- 
plished by  what  is  known  as  the  penetration  method,  in  which 
the  wearing  course  is  treated  after  being  laid.  As  working 
facilities  grow  better  and  traffic  conditions  more  severe  this  will 
be  gradually  superseded  by  the  mixing  method,  in  which  the 
road  stone  constituting  the  wearing  course  is  covered  with  the 
binding  medium  before  being  laid  on  the  road.  The  first  im- 
portant step  toward  the  city  pavement  form  of  construction 
will  then  have  been  taken,  and  the  construction  of  a  more  rigid 
foundation  by  the  use  of  an  hydraulic  cement  will  naturally 
follow,  as  will  also  other  details  of  construction  approaching 
that  of  the  city  pavement.  In  individual  cases  this  develop- 
ment has  already  taken  place,  but,  like  men  who  are  intellec- 
tually in  advance  of  their  time,  they  are  not  representative  of 
the  main  portion. 

The  most  direct  cause  of  this  evolution  of  the  macadam  road 
will  be  the  continued  rapid  growth  of  automobile  traffic  and  the 
adoption  of  the  motor  van  for  commercial  transportation. 
Statistics  show  the  following  increase  in  number  of  motor 
vehicles  manufactured  in  the  United  States  during  the  years 
1900  to  1909  and  it  is  only  reasonable  to  suppose  that  this  is 
an  indication  of  what  the  future  rate  of  increase  is  apt  to  be. 

APPROXIMATE  PRODUCTION   OF  AUTOMOBILES 
IN  THE  UNITED  STATES. 


Year. 

Number. 

Year. 

Number. 

1900 
1901 

4,192 

10,000 

1906 

30,000 
40,000 

1902 
1903 

15,000 

19,400 

1907 
1908 

40,000 

1904 

25,000 

1909 

114,900 

It  is  estimated  that  there  were  40,000  motor  vehicles  in  the 
United  States  at  the  close  of  1902.     What  the  number  is  at 


24  DUST   PREVENTIVES   AND    ROAD   BINDERS 

present  is  problematical,  but  as  the  Census  Report  of  1908  shows 
that  during  1907  and  1908  the  number  of  automobiles  exported 
amounted  to  5339  against  2121  imported,  it  is  evident  that  for 
the  ten  years  enumerated  above  there  was  a  comparatively 
small  diminution  in  numbers,  due  to  exports.  The  estimated 
total  production  since  1902  is  324,300  which  added  to  the 
40,000  above  mentioned  gives  a  grand  total  of  364,300.  A 
]sm  proportion,  at  least  two-thirds,  of  these  machines  are  pr-ob- 
a^iy  in  use  in  this  country  at  the  present  time.  During  1909 
there  were  approximately  270  firms  engaged  in  the  manufacture 
of  motor  vehicles  and  about  125,000  men  employed  in  the  in- 
dustry. The  total  value  of  the  machines  produced  amounted 
to  about  $135,000,000,  for  that  year.  A  large  increase  in  pro- 
duction is  indicated  for  some  years  to  come. 

An  increase  in  motor  vans  capable  of  carrying  heavy  loads 
is  also  an  assured  fact  for  economic  reasons.  It  has  been  esti- 
mated that  in  England  under  favorable  conditions  the  cost 
of  haulage  per  ton  mile  for  gasoline  delivery  vans  lies  between 
twelve  cents  for  light  loads  and  five  to  six  cents  for  heavy  loads. 
For  the  steam  tractor,  an  innovation  which  has  not  yet  been 
adopted  in  the  United  States,  this  figure  is  reduced  to  two  and 
one-half  cents  per  ton  mile  in  comparison  with  six  and  one- 
half  cents  for  horse  drawn  vehicles.  In  this  country,  where  the 
price  of  gasoline  is  much  cheaper,  it  is  probable  that  even 
greater  differences  in  favor  of  the  motor  vehicle  will  be  shown 
as  this  form  of  traffic  develcps. 

Owing  to  the  exceedingly  heavy  loads  which  will  sooner  or 
later  be  transported  over  our  roads  in  this  way  the  necessity 
will  arise  for  a  more  stable  foundation  than  that  of  a  newly 
constructed  macadam  road,  and  it  would  seem  highly  probable 
that  the  cement  grouted  foundation  will  be  the  one  to  be  em- 
ployed. If  motor  traffic  alone  were  to  be  considered,  a  road 
built  entirely  of  cement  concrete  might  prove  the  most  satis- 
factory and  economical  form  for  the  future.  For  mixed  traffic, 
however,  such  a  road  is  by  no  means  ideal  and  as,  in  spite  of  the 
increase  in  motor  vehicles,  the  number  of  horse  drawn  vehicles 


DUST  PREVENTION  AND   ROAD   PRESERVATION  25 

does  not  seem  to  be  decreasing,  a  form  of  road  best  suited  to 
meet  the  requirements  of  both  classes  of  traffic  will  have  to  be 
considered.  The  type  of  road  with  cement  concrete  foundation 
and  bituminous  concrete  surface  as  described  above  would, 
therefore,  seem  in  the  light  of  our  present  knowledge  to  be  best 
suited  to  meet  these  requirements.  It  is,  of  course,  possible 
that  new  materials  of  construction  will  be  discovered  or  invented 
which  will  prove  more  satisfactory,  but  at  the  present  time  there 
are  no  indications  that  this  will  happen. 

Summary  and  Conclusions.  —  In  this  chapter  the  problems  of 
dust  prevention  and  road  preservation  have  been  considered  in 
detail  and  their  causes  and  effects  studied.  The  relations  be- 
tween the  two  problems  have  been  discussed  and  also  methods 
of  solving  them.  The  importance  of  the  dust  problem  has  been 
shown  by  a  consideration  of  the  undesirable  effects  of  road 
dust  upon  public  health  and  comfort,  upon  personal  and  real 
property,  upon  vegetation  of  all  kinds  and  upon  the  road  itself. 

The  causes  of  road  dust  formation  are  the  chemical,  physical 
and  mechanical  agencies  which  produce  wear  of  the  road,  and 
the  transportation  of  extraneous  fine  material  to  the  road  sur- 
face from  outside  sources.  As  road  dust  is  largely  a  product  of 
road  wear  it  is  evident  that  the  problems  of  dust  prevention 
and  road  preservation  are  closely  associated. 

The  most  important  dust  raising  and  road  destroying  factor 
of  modern  times  is  the  fast  moving  motor  car,  owing  to  air  cur- 
rents generated  in  its  rear  and  to  the  great  tractive  force  exerted 
by  its  rear  wheels  upon  the  road  surface.  Any  solution  of  the 
two  problems  must,  therefore,  deal  largely  with  methods  designed 
to  overcome  these  tendencies  of  the  automobile,  although  the 
effect  of  impact  and  abrasion  of  ordinary  traffic  must  also  be 
considered,  and  especially  the  combined  effect  of  both  classes  of 
traffic. 

There  are  three  general  methods  of  reducing  dust  formation 
which  should  be  considered  in  attempting  a  solution  of  this 
problem:  (i)  by  the  sanitary  removal  of  dust  from  road  surfaces: 
(2)  by  the  retention  of  dust  upon  the  road  surface,  and  (3)  by 


26  DUST   PREVENTIVES   AND    ROAD   BINDERS 

the  prevention  of  dust  formation.  Any  or  all  of  these  methods 
may  be  employed  to  solve  the  problem  of  road  preservation. 
The  most  promising  solution  would  seem  to  lie  in  the  treatment 
of  roads  with  chemical  substances  known  as  dust  preventives 
and  road  Binders,  which  may  be  applied  to  the  surface  or  in  the 
body  of  the  road  according  to  circumstances.  The  importance 
of  other  methods  described  should,  however,  never  be  lost  sight  of, 
for  it  is  only  by  a  combination  of  methods  that  the  two  problems 
can  be  successfully  solved. 

The  necessity  for  specific  information  on  the  part  of  the  road 
engineer  concerning  the  composition  and  properties  of  chemical 
dust  preventives  and  road  binders  as  related  to  their  use,  has 
been  discussed  and  it  has  been  stated  that  many  experimental 
failures  and  much  confusion  as  to  the  cause  of  such  failures  are 
directly  attributable  to  this  lack  of  knowledge. 

In  conclusion  the  most  probable  form  of  road  which  will  be 
developed  in  the  future  has  been  considered,  and  it  has  been 
shown  that  indications  point,  toward  the  evolution  of  the  modern 
broken  stone  road  to  one  having  a  cement  concrete  base  and  a 
bituminous  concrete  surface. 


CHAPTER  II. 

CLASSIFICATION  OF  DUST   PREVENTIVES  AND   ROAD 
BINDERS. 

DUST  preventives  may  be  conveniently  classified  in  two  ways, 
i.e.,  according  to  the  purpose  for  which  they  are  used,  which 
depends  to  a  great  extent  upon  their  physical  properties,  or 
according  to  their  chemical  composition.  A  combination  of  both 
classifications  is  probably  the  most  satisfactory  way  of  consider- 
ing them,  and  this  course  will  be  pursued  in  the  following  chapter, 
when  individual  materials  are  discussed.  Before  doing  this,  how- 
ever, it  may  be  well  to  briefly  describe  each  method  separately. 

Classification  According  to  Purpose  for  Which  Used.  —  In 
this  classification  the  names  dust  preventives  and  road  binders 
at  once  suggest  two  divisions.  It  has  been  stated  that  dust 
preventives  or  palliatives  may  be  considered  as  temporary 
binding  mediums  for  dust  particles,  and  road  binders  as  more 
or  less  permanent  binding  mediums  employed  for  the  purpose 
of  holding  together  the  mineral  fragments  constituting  the  body 
or  at  least  the  surface  of  the  road.  Such  materials  may  be 
applied  either  to  the  finished  surface  or  internally  to  the  road 
during  construction  or  resurfacing.  In  the  former  case,  as 
would  naturally  be  expected,  the  results  are  of  a  less  lasting 
character  than  in  the  latter.  Binders  applied  to  the  surface 
will  of  course  disappear  more  or  less  rapidly  according  to  their 
depth  of  penetration,  as  the  road  surface  wears  down,  while 
those  applied  in  the  construction  of  roads  should  prove  effective 
as  long  as  the  road  itself  lasts  or  until  the  wearing  surface  is 
destroyed.  They  may,  therefore,  be  considered  as  semi-per- 
manent or  permanent  compared  with  the  dust  palliatives  or 
temporary  binders.  Three  main  classes  are  thus  established, 
although  no  sharply  defined  lines  can  be  drawn  between  them, 
owing  to  the  fact  that  some  materials  merge  from  one  class  into 

27 


28  DUST   PREVENTIVES    AND    ROAD    BINDERS 

another  according  to  their  inherent  properties  or  to  the  quantity 
that  is  applied  at  any  one  time.  The  degree  of  concentration 
of  the  binding  base  contained  may  also  cause  certain  materials 
to  be  classified  under  more  than  one  heading.  For  all  practical 
purposes,  however,  the  classification  mentioned  above  will  be 
followed  and  this  method  may  be  used  as  a  sub-classification 
when  arranging  the  materials  according  to  their  chemical  com- 
position. We  may,  therefore,  consider  dust  preventives  and 
road  binders  as  being  either: 

(1)  Temporary  binders. 

(2)  Semi-permanent  binders. 

(3)  Permanent  binders. 

Temporary  Binders.  —  The  temporary  binders  are  for  the 
most  part  applied  to  road  surfaces  solely  for  the  purpose  of 
laying  dust,  both  that  produced  from  the  road  itself  and  that 
brought  in  from  outside  sources.  By  thus  keeping  a  film  or 
layer  of  fine  material  upon  the  road  surface  they  may  also  tend 
to  preserve  the  under  surface  of  the  road  from  wear  and  in  the 
case  of  broken  stone  roads  from  the  disintegration  which  would 
result  from  the  removal  of  fine  material  from  the  interstices 
between  the  coarser  fragments  of  the  wearing  surface.  On 
roads  and  pavements  that  are  frequently  cleaned  they  are 
ordinarily  employed  to  lay  the  dust  just  before  cleaning,  in 
order  that  it  may  be  removed  without  being  dispersed  into  the 
atmosphere.  The  temporary  binders  from  their  very  nature 
must  be  applied  at  frequent  intervals,  sometimes  as  often  as 
two  or  three  times  a  day,  and  sometimes  at  periods  varying 
from  one  to  four  weeks. 

In  order  that  they  may  be  employed  at  all,  it  is,  for  reasons 
of  economy,  necessary  that  they  be  capable  of  easy  application. 
The  only  economical  method  of  applying  such  materials  is  by 
means  of  a  sprinkling  cart  and  they  must,  therefore,  be  thin  liq- 
uids, viscous  liquids  miscible  with  water,  or  solids  readily  soluble 
in  water.  Their  power  of  holding  the  dust  particles  together 
may  be  due  to  one  of  two  properties,  that  of  capillary  attraction 


CLASSIFICATION    OF   DUST   PREVENTIVES  29 

or  to  the  presence  of  a  certain  amount  of  true  binding  base.  In 
the  first  case  they  simply  moisten  the  surface  of  the  particles 
which  are  then  held  together  by  the  capillary  attraction  of  the 
films  of  liquid  between  them.  In  the  second  case  the  particles 
are  actually  cemented  together  by  films  of  sticky  or  glue-like 
materials.  In  certain  rather  exceptional  cases,  temporary 
binders  may  react  chemically  with  the  fine  mineral  fragments 
of  the  road  to  produce  binding  films  of  a  colloid  or  glue-like 
character.  Their  dust  laying  effect  is  of  short  duration  because 
of  the  fact  that  they  either  volatilize  readily,  are  carried  away 
by  rains,  or  soon  become  saturated  with  dust,  thus  being 
rendered  incapable  of  holding  down  fresh  dust  which  may  be 
formed  or  brought  upon  the  road.  Those  that  do  not  vola- 
tilize and  are  of  an  inherently  sticky  nature,  if  insoluble  in 
water,  concentrate  upon  the  road  surface  after  a  number  of 
applications  and  thus  become  in  effect  semi-permanent  binders. 
This  is  the  most  valuable  type  of  dust  palliative  for  use  on 
roads  which  are  not  cleaned  frequently. 

The  temporary  binders  are  employed  mainly  on  city,  park 
and  suburban  roads  where  dust  from  outside  sources  has  to  be 
taken  care  of,  and  are  often  used  in  conjunction  with  the  other 
classes  of  binders.  As  has  been  said  they  are  applied  by  means 
of  a  sprinkling  cart  in  the  same  way  that  water  is  applied. 
No  definite  rules  can  be  laid  down  in  regard  to  the  frequency 
with  which  they  should  be  employed,  as  this  is  not  only  depend- 
ent upon  the  physical  properties  of  each  material*  but  also  upon 
the  local  conditions  to  which  the  road  is  subjected.  This 
subject  will  be  discussed  elsewhere  at  greater  length. 

Semi-Permanent  Binders.  -  -  The  semi-permanent  binders  are 
applied  to  road  surfaces  mainly  for  the  purpose  of  preserving 
the  road  from  wear,  although  they  also  serve  as  dust  layers  for 
some  time  after  application,  and,  of  course,  prevent  excessive 
dust  formation  from  the  materials  of  which  the  road  is  com- 
posed. Their  property  of  laying  dust,  especially  that  from 
outside  sources,  is  limited  by  their  capacity  for  absorbing  the 
dust.  A  single  application  of  these  materials  should  preserve 


30  DUST   PREVENTIVES   AND    ROAD    BINDERS 

the  road  surface  from  disintegration  and  appreciably  lessen 
dust  formation  for  a  period  of  at  least  one  year.  They  cannot, 
however,  be  expected  to  keep  a  road  dustless  for  this  length  of 
time  where  any  considerable  quantity  of  dust  from  outside 
sources  is  encountered. 

The  semi-permanent  binders  are  liquids  containing  appreci- 
able quantities  of  true  binding  materials  and  are  applied  cold  or 
hot  according  to  their  viscosity  at  ordinary  temperatures.  If 
sufficiently  fluid  to  apply  cold,  certain  of  their  constituents 
should  be  of  a  rather  volatile  nature,  or  else  show  a  tendency 
to  harden  upon  exposure.  In  the  former  case,  ease  of  appli- 
cation is  obtained  at  the  expense  of  the  material  lost  by  vola- 
tilization, the  true  binding  base  being  merely  diluted  by  the 
volatile  constituents,  and  left  upon  the  road  after  they  have 
disappeared. 

Cold  applications  may  usually  be  made  by  means  of  an 
ordinary  sprinkling  cart,  but  hot  applications  require  hand 
labor  or  else  especially  constructed  sprinkling  contrivances. 
Distributing  carts  carrying  spraying  devices  and  so  equipped 
that  the  material  may  be  heated  in  the  cart  and  forced  upon  the 
road  surface  under  air  or  steam  pressure  are  extensively  em- 
ployed in  England  and  France.  A  number  oi  these  machines 
have  been  imported  to  this  country  and  are  now  being  used  in 
the  surface  treatment  of  roads. 

As  the  semi-permanent  binders  seldom  prove  effective  for  over 
a  year,  they  m'ay  best  be  applied  in  the  early  spring  at  the  be- 
ginning of  the  dusty  season.  They  rarely  withstand  the  severi- 
ties of  winter  weather  and  winter  traffic,  and  unless  applied  at 
the  time  mentioned  are  not  apt  to  give  satisfactory  results  for 
even  a  year.  They  must  of  course  be  applied  annually  but 
never  to  a  worn-out  or  badly  rutted  surface.  In  most  cases  it  is 
desirable  and  in  some  absolutely  necessary  to  remove  all  loose 
dust  and  detritus  from  the  road  surface  before  applying  them, 
and  any  repairs  required  should  be  made  before  application. 
These  materials  give  best  results  on  broken  stone  or  gravel  roads 
which  are  not  subjected  to  exceedingly  severe  traffic  conditions, 


CLASSIFICATION   OF  DUST   PREVENTIVES  3 1 

but  which  require  some  medium  to  consolidate  and  hold  down 
their  wearing  surface.  Some  of  them  have  been  employed  in 
the  treatment  of  earth  roads,  but  it  is  usually  better  practice  to 
reconstruct  such  roads  with  the  addition  of  a  suitable  permanent 
binder,  which  will  add  to  their  stability. 

Permanent  Binders.  —  Permanent  binders  are  employed  in 
the  construction  of  roads  and  pavements  primarily  for  the  pur- 
pose of  holding  the  coarser  wearing  particles  together.  By  pre- 
venting disintegration  and  reducing  wear  they  also  reduce  dust 
formation  from  the  road  material  itself.  They  are  heavy  bind- 
ing mediums  adding  to  the  stability  of  the  road  but  having  little 
absorptive  capacity  for  dust.  They  should  prove  effective  until 
the  wearing  surface  of  the  road  is  actually  worn  out. 

Such  binders  include  the  very  viscous  or  semi-solid  bituminous 
cements  which  produce  a  well-bound  resilient  concrete  when 
incorporated  in  a  mineral  aggregate,  and  mineral  cements  which 
produce  a  rigid  concrete.  The  former  reduce  wear  through  the 
cushioning  effect  which  they  exert  upon  the  wearing  fragments, 
while  the  latter  actually  take  up  a  considerable  amount  of  wear 
themselves  and  are  effective  because  of  the  hardness  and  density 
of  the  concrete  which  they  produce.  Bituminous  cements  are 
employed  in  the  construction  of  nearly  all  classes  of  roads  and 
pavements,  while  mineral  cements  are  almost  exclusively  em- 
ployed in  pavement  work.  Either  type  of  material  may  be  used 
throughout  the  entire  depth  of  road  or  only  in  the  wearing  sur- 
face. Both  can  often  be  employed  to  advantage  in  the  same 
road,  and  when  this  is  the  case  the  mineral  cement  is  usually 
worked  into  the  foundation  and  the  bituminous  cement  into  the 
wearing  surface. 

Permanent  binders  may  be  applied  to  the  road  proper  while 
under  construction,  or  they  may  be  mixed  with  the  road  material 
before  being  laid.  Either  method  may  be  carried  out  by  hand 
or  mechanical  labor.  Bituminous  cements,  unless  containing 
large  quantities  of  volatile  materials,  should  be  of  such  consist- 
ency as  to  require  heating  before  being  applied  and  it  is  often 
desirable  to  heat  the  mineral  aggregate  before  they  are  incor- 


32  DUST  PREVENTIVES   AND   ROAD   BINDERS 

porated  with  it.  This,  however,  is  only  done  when  the  mixing 
method  is  followed.  Permanent  binders  are  employed  to  best  ad- 
vantage on  highways  subjected  to  rather  severe  traffic  conditions 
and  their  use  should  always  be  supplemented  by  that  of  a  tem- 
porary binder  or  dust  palliative  where  outside  dust  is  excessive. 
Classification  According  to  Chemical  Characteristics. —  Bear- 
ing in  mind  the  explanations  given  above  as  to  what  is  meant 
by  the  terms  temporary,  semipermanent  and  permanent  bind- 
ers, and  the  brief  descriptions  of  the  various  physical  proper- 
ties of  these  three  classes  of  materials  as  regards  their  use,  we 
may  take  up  their  further  classification  according  to  chemical 
characteristics.  This  is  a  purely  arbitrary  matter  depending 
upon  the  point  of  view  of  the  classifier.  For  a  number  of  reasons 
it  has  seemed  best  to  the  author  to  consider  dust  preventives  and 
road  binders  under  two  broad  headings  and  to  divide  each  of 
these  divisions  into  two  general  subdivisions  as  follows: 

I.  Non-bituminous  materials. 

(a)  Inorganic. 

(b)  Organic. 

II.  Bituminous  materials. 

(a)  Petroleums,    petroleum   products    and    solid    native 
bitumens. 

(b)  Tars  and  tar  products. 

The  convenience  of  this  method  of  classification  will  become 
apparent  as  the  subject  is  developed.  Each  of  the  subdivisions 
may  now  be  considered  under  the  headings  temporary,  semi- 
permanent and  permanent  binders. 

Inorganic  Materials.  —  Chemically  speaking,  inorganic  sub- 
stances are  differentiated  from  organic  by  the  fact  that  the  car- 
bon atom  is  either  absent  from  their  molecules  or  else  exists  in 
such  a  state  of  combination  that  the  material  cannot  be  con- 
sidered as  a  hydrocarbon  or  hydrocarbon  derivative.  Thus 
water,  whose  chemical  symbol  is  H20,  and  common  salt  (NaCl) 
contain  no  carbon  atom  in  their  molecules  and  are,  therefore, 
inorganic  materials.  On  the  other  hand  limestone  or  calcium 


CLASSIFICATION   OF  DUST  PREVENTIVES  33 

carbonate  (CaC03),  while  containing  a  carbon  atom,  cannot  be 
considered  as  a  hydrocarbon  derivative  and  is  also  classified  as 
inorganic. 

Among  the  temporary  binders  water  is  the  first  substance  which 
should  be  mentioned.  Solutions  of  such  chemical  salts  as  cal- 
cium chloride  and  magnesium  chloride  whose  hygroscopic  proper- 
ties are  made  use  of  for  the  purpose  of  increasing  the  dust  laying 
efficiency  of  water  come  next  in  order.  There  seem  to  be  no 
semipermanent  binders  among  the  inorganic  materials  unless 
solutions  of  salts,  which  are  supposed  to  react  with  each  other  or 
with  the  fine  mineral  particles  upon  the  road  surface  to  form 
colloidal  binding  films,  may  be  so  considered.  Such  materials 
have  not  been  employed  to  a  sufficient  extent  to  warrant  any  very 
definite  opinion  as  to  which  of  the  two  classes  they  should  belong. 
Sodium  silicate  solutions  alone  or  employed  in  connection  with 
water  soluble  salts  of  calcium  and  magnesium  may  be  taken  as 
typical  of  this  class  of  materials. 

The  permanent  inorganic  binders  are  the  various  hydraulic 
cements  which  produce  hard  and  rigid  concretes.  Among  them 
may  be  mentioned  natural  cements,  Portland  'cements  and  slag 
cements.  They  are  the  most  powerful  known  road  binders, 
and  when  employed  in  considerable  quantity  produce  with  the 
mineral  fragments  of  the  road  a  true  monolithic  surface.  This 
is  an  important  characteristic  which  effects  the  results  obtained 
by  their  use  as  compared  to  those  obtained  from  the  use  of  the 
heavy  bituminous  cements. 

Non-Bituminous  Organic  Materials. —  Among  the  temporary 
binders  of  this  division  may  be  mentioned  such  vegetable  oils  as 
oil  of  aloes  whose  dust  laying  properties  are  similar  to  those  of 
water.  That  is,  they  contain  little  or  no  true  binding  base  but 
hold  the  dust  particles  together  through  capillary  attraction. 
Being  of  a  less  volatile  nature  than  water  one  application  will 
keep  down  the  dust  for  a  much  longer  time.  In  common  with 
most  poor  binding  oils  they  have  certain  undesirable  properties 
which  will  be  discussed  in  Chapter  V.  Animal  fats  such  as 
waste  grease  obtained  from  wool  scourings  may  be  considered  as 


34  DUST  PREVENTIVES   AND   ROAD   BINDERS 

temporary  binders  and  show  the  same  general  characteristics  in 
so  far  as  road  treatment  is  concerned.  Some  of  these  materials 
are  applied  in  their  natural  condition  but  more  often  in  com- 
bination with  other  materials  in  the  form  of  emulsions.  They 
are  mainly  employed  in  patented  road  preparations. 

As  an  example  of  the  semipermanent  binders  may  be  men- 
tioned concentrated  waste  sulphite  liquors,  obtained  and  pre- 
pared from  the  waste  products  produced  in  the  manufacture 
of  wood  pulp  according  to  the  sulphite  process.  Waste  molasses 
residues  when  combined  with  quicklime  may  also  be  noted 
among  this  class  of  materials.  These  substances  either  con- 
tain an  appreciable  amount  of  true  binding  base  or  are  inher- 
ently sticky  liquids.  Most  of  them  are  somewhat  soluble  in 
water  and  cannot,  therefore,  be  employed  as  permanent  binders 
without  the  addition  of  a  waterproofing  agent,  no  matter  how 
powerfully  they  bind  the  mineral  fragments  of  the  road  together. 
With  the  exception  of  the  two  mentioned  and  possibly  a  few 
others,  they  are  of  interest  only  because  they  have  been  sug- 
gested for  road  work  and  not  because  they  have  been  employed 
for  this  purpose  to  any  extent. 

At  the  present  time  there  would  seem  to  be  no  non-bitumi- 
nous organic  materials  which  might  be  considered  as  perma- 
nent binders,  except  perhaps  compounds  of  rosin  with  certain 
inorganic  bases,  which  will  be  described  in  their  place. 

Petroleums,  Petroleum  Products  and  Solid  Native  Bitumens.  — 
As  the  greater  part  of  this  book  will  be  devoted  to  a  consid- 
eration of  bituminous  road  materials,  it  is  unnecessary  in  this 
chapter  to  do  more  than  note  representative  types  of  the  sub- 
divisions of  the  classification  described. 

The  temporary  binders  may  be  represented  by  crude  paraffin 
petroleums,  petroleum  distillates  and  semiasphaltic  and  asphaltic 
oil  emulsions.  The  first  two  materials  like  the  vegetable  oils 
show  little  or  no  true  binding  properties  but  are  dependent  upon 
their  moistening  property  to  keep  down  the  dust  particles.  They 
are  essentially  lubricants  and  when  present  in  any  considerable 
amount  are  apt  to  disintegrate  the  road  surface  rather  than 


CLASSIFICATION   OF   DUST   PREVENTIVES  35 

bond  it.  A  better  class  of  temporary  binders  is  found  in  the 
asphaltic  oil  emulsions  which  often  prove  to  be  excellent  road 
preservatives. 

Semipermanent  binders  may  be  represented  by  the  heavy 
semiasphaltic  and  asphaltic  petroleums  and  the  liquid  resid- 
uums  obtained  from  such  oils.  According  to  their  viscosity, 
percentage  of  volatile  oils  and  asphaltic  contents  they  merge 
gradually  into  the  permanent  binder  class. 

Semisolid  and  very  viscous  asphaltic  and  semiasphaltic  oil 
residuums,  as  well  as  native  asphalts  and  solid  native  bitumens 
of  an  asphaltic  character,  make  up  the  permanent  binder  class. 
The  two  former  are  the  most  commonly  employed  in  road  con- 
struction and  the  two  latter  in  city  pavements.  Of  late,  how- 
ever, both  the  asphalts  and  other  solid  native  bitumens  when 
cut  with  comparatively  large  amounts  of  oil  fluxes  have  been 
used  to  some  extent  in  road  work.  Such  mixtures  exhibit 
properties  quite  similar  to  the  heavy  asphaltic  oil  residuums. 

Tars  and  Tar  Products.  —  These  materials  include  the  tarry 
liquids  produced  from  the  destructive  distillation  of  bitumi- 
nous coal  and  petroleum  oils,  and  their  refined  products.  Many 
other  materials  such  as  wood,  bone,  etc.,  when  subjected  to 
this  process  produce  artificial  bitumens  known  as  tars  but  as 
these  are  seldom  if  ever  employed  as  dust  preventives  or  road 
binders,  they  will  be  given  but  passing  notice. 

Among  the  temporary  binders  of  this  class  may  be  men- 
tioned tar  distillates,  such  as  creosote  oils,  very  watery  crude 
tars,  such  as  oil  gas  or  water  gas  tar,  and  tar  emulsions.  Tar 
distillates  and  the  crude  watery  tars  may  be  compared  to  the 
petroleum  distillates  and  crude  paraffin  petroleums,  and  the  tar 
emulsions  with  the  semiasphaltic  and  asphaltic  oil  emulsions  so 
far  as  their  dust  laying  and  road  binding  properties  are  con- 
cerned. From  a  chemical  standpoint,  however,  they  are  quite 
different. 

The  heavier  crude  tars  and  partially  refined  or  fluid  tar  residu- 
ums may  be  considered  as  semipermanent  binders  and  are  com- 
parable with  the  crude  asphaltic  oils  and  fluid  oil  residuums. 


36  DUST   PREVENTIVES   AND   ROAD   BINDERS 

They  also  merge  gradually  into  the  permanent  binders,  accord- 
ing to  their  viscosity  and  relative  volatile  oil  and  pitch  contents. 

The  permanent  binders  of  this  class  of  materials  comprise 
the  very  viscous  and  semisolid  pitch  residues  obtained  from 
fractional  distillation  of  the  crude  tars.  Such  products  are 
entirely  analogous  to  the  heavy  oil  residuums  and  oil  pitches 
mentioned  under  the  natural  bitumens.  Tar  pitches,  like  as- 
phalts, have  been  employed  to  a  considerable  extent  in  the 
construction  of  city  pavements. 

Summary  and  Conclusions.  —  In  this  chapter  the  classification 
of  dust  preventives  according  to  their  use  and  chemical  char- 
acteristics has  been  described.  The  two  methods  of  classifi- 
cation have  been  combined  and  representative  types  of  materials 
have  been  noted.  Temporary  binders  are  those  which  are  in- 
tended to  be  applied  at  frequent  intervals;  semipermanent 
binders  are  materials  which  upon  one  application  prove  effective 
for  approximately  one  year  or  at  least  throughout  a  dusty  season ; 
and  permanent  binders  are  those  which  last  as  long  as  the  wearing 
surface  of  the  road  remains  intact.  Materials  holding  interme- 
diate positions  also  occur  so  that  this  division  is-not  a  sharp  one. 

For  the  sake  of  reference  this  classification  is  given  below  in 
tabular  form.  In  this  table  it  has  not  been  considered  necessary 
to  include  all  known  dust  preventives  and  road  binders,  and 
only  the  most  important  or  representative  types  have,  therefore, 
been  given :  — 

CLASSIFICATION    OF    DUST  PREVENTIVES  AND  ROAD   BINDERS. 
I.   Non-bituminous  materials. 
(i)  Inorganic. 

(a)  Water. 

Calcium  chloride  and  other  hygroscopic  salts. 

(b)  Sodium    silicate    and    other    chemicals    capable    of 
reacting  with  each  other  or  with  the  road  fragments 
to  form  colloidal  binding  films. 

Rock  and  slag  powders. 

(c)  Portland  and  other  hydraulic  cements. 


CLASSIFICATION   OF   DUST   PREVENTIVES  3/ 

(2)  Organic. 

(a)  Oil  of  aloes  and  other  vegetable  oils. 
Wool  scourings  and  other  animal  greases. 

(b)  Concentrated  waste  sulphite  liquors. 
Waste  molasses  residues. 

(c)  Resinates. 

II.   Bituminous  materials. 

(1)  Petroleums,  petroleum  products  and  solid  native  bitumens. 

(a)  Crude  paraffin  petroleums. 
Petroleum  distillates. 

Semiasphaltic  and  asphaltic  oil  emulsions. 

(b)  Viscous  crude  semiasphaltic  and  asphaltic  petroleums. 
Liquid  semiasphaltic  and  asphaltic  oil  residuums. 

(c)  Very  viscous  and  semisolid  semiasphaltic  and  asphal- 
tic oil  residuums  or  oil  pitches. 

Asphalts   and   other   solid   native   bitumens   of   an 
asphaltic  nature. 

(2)  Tars  and  tar  products. 

(a)  Crude  water  gas  tars  or  oil  gas  tars. 
Tar  oils  or  distillates. 
Emulsions  containing  tar. 

(b)  Crude  coal  tars. 
Liquid  tar  residuums. 

(c)  Very  viscous  tar  residuums.      * 
Tar  pitches. 

In  conclusion  it  may  be  well  to  mention  the  fact  that  dust 
preventives  and  road  binders  as  found  upon  the  market  do  not 
always  consist  of  one  class  of  materials  but  may  be  mixtures  of 
two  or  more  classes.  They  may  also  have  been  chemically 
treated  in  various  ways  so  as  to  modify  or  alter  their  original 
properties.  Such  preparations  cannot  well  be  classified  under 
any  one  of  the  headings  given  above  and  it  is  often  an  exceedingly 
difficult  matter  to  determine  just  what  the  preparation  is  com- 
posed of.  Thus  an  asphalt  or  other  solid  native  bitumen  may 


38  DUST  PREVENTIVES  AND   ROAD   BINDERS 

have  been  fluxed  with  an  oil  residuum  or  a  refined  tar  in  such 
a  manner  as  to  conceal  its  identity  and  various  other  deceptive 
combinations  may  be  encountered.  Certain  methods  of  exami- 
nation have,  however,  been  devised  which  are  of  great  assistance 
in  identifying  and  classifying  such  materials  and  these  methods 
will  be  described  later. 


CHAPTER  III. 
INORGANIC  DUST  PREVENTIVES  AND  ROAD  BINDERS. 

As  has  been  stated  in  Chapter  II,  non-bituminous  dust  pre- 
ventives and  road  binders  may  be  divided  into  two  main  classes, 
inorganic  and  organic.  In  this  chapter  and  the  next  the  indi- 
vidual materials  composing  the  first  class  will  be  taken  up  and 
discussed,  according  to  their  arrangement  as  previously  given. 
It  has  seemed  well  to  the  author  to  also  include  the  methods  of 
application  and  relative  value  of  these  substances  in  order  to 
prepare  the  way  for  the  exclusive  consideration  of  bituminous 
materials  in  the  succeeding  chapters.  By  so  doing,  much  con- 
fusion will  be  avoided  and  a  better  idea  of  the  entire  subject  will 
be  obtained  than  if  they  are  considered  together. 

Water.  —  Water  is  undoubtedly  the  first  material  ever  used 
for  the  purpose  of  laying  dust,  and  in  cities  and  thickly  settled 
suburban  districts  is  at  present  the  most  generally  employed. 
During  hot  dry  weather  its  use  has  seldom  proved  satisfactory, 
owing  to  its  rapid  evaporation.  Frequent  and  heavy  applica- 
tions are  often  required  to  keep  the  dust  down  and  in  many  local- 
ities where  traffic  is  heavy,  it  is  practically  impossible  to  obtain 
good  results  by  the  use  of  water  alone.  The  cost  of  frequent 
sprinklings  with  water  is  a  considerable  item;  and  when  the  fact 
is  taken  into  account  that  at  the  end  of  a  season  but  little  per- 
manent benefit  has  been  derived  from  its  use,  it  will  be  seen  that 
dust  laying  by  this  method  is  by  no  means  economical.  When 
too  heavy  applications  are  made  to  broken  stone  roads  the  surface 
is  apt  to  be  gullied,  and  the  dust  converted  for  the  time  being 
into  mud.  As  has  been  stated,  the  principal  value  of  water  in 
laying  dust  consists  in  the  mechanical  bond  produced  by  force 
of  capillarity  when  two  wet  surfaces  are  brought  in  contact. 
In  proper  quantities  its  presence  is  necessary  to  preserve  the 

39 


40  DUST  PREVENTIVES   AND   ROAD   BINDERS 

cementing  power  of  the  fine  particles  of  ordinary  broken  stone 
roads,  and  it  often  reacts  with  such  particles  to  form  colloidal  or 
crystalline  binding  materials  which  hold  the  road  surface  in  place. 
It  will  not,  however,  produce  this  effect  upon  all  kinds  of  rock 
dust,  and  this  fact  has  been  made  the  basis  of  methods  for  deter- 
mining the  relative  cementing  value  of  different  rock  powders. 

A  practical  physical  test  for  determining  the  cementing 
value  was  first  developed  by  Page,  working  in  cooperation 
with  the  Massachusetts  State  Highway  Commission,  and 
further  under  Page  and  Cushman  in  the  Division  of  Tests, 
Bureau  of  Chemistry,  U.  S.  Department  of  Agriculture,  and 
later  in  the  laboratories  of  the  U.  S.  Office  of  Public  Roads. 
The  underlying  reasons  for  the  cementing  value  of  rock  dusts 
and  the  curious  variations  that  are  noted  in  this  property  were 
developed  in  the  exhaustive  researches  of  Cushman  extending 
over  a  number  of  years.  For  the  fullest  information  with 
regard  to  this  subject  the  original  papers  *  should  be  referred  to. 

Water  is  ordinarily  applied  by  means  of  horse  drawn  sprin- 
kling carts  although  self-propelled  sprinklers  have  also  been 
employed  to  some  extent.  These  carts  vary  in  capacity  from 
300  to  1000  gallons  and  over.  The  water  should  preferably  be 
distributed  in  the  form  of  a  spray  and  not  forced  directly  upon 

*  "On  the  Cause  of  the  Cementing  Values  of  Rock  Powders  and  the  Plasticity 
of  Clays,"  A.  S.  Cushman,  J.  Am.  Chem.  Soc.,  1903,  Vol.  XXV,  No.  5,  pp.  451- 
468. 

"The  Testing  of  Road  Materials,"  L.  W.  Page  and  A.  S.  Cushman,  Bull.  79, 
Bureau  of  Chemistry,  U.  S.  Dept.  Agriculture. 

"The  Colloid  Theory  of  Plasticity,"  A.  S.  Cushman,  Trans.  Am.  Ceramic  Soc., 
1904,  Vol.  VI,  pp.  3-16. 

"The  Useful  Properties  of  Clays,"  A.  S.  Cushman,  Circ.  17,  Bureau  of  Chemistry, 
U.  S.  Dept.  Agriculture. 

"The  Cementing  Power  of  Road  Materials,"  L.  W.  Page  and  A.  S.  Cushman, 
Bull.  85,  Bureau  of  Chemistry,  U.  S.  Dept.  Agriculture. 

"The  Effect  of  Water  on  Rock  Powders,"  A.  S.  Cushman,  Bull.  92,  Bureau  of 
Chemistry,  U.  S.  Dept.  Agriculture. 

"A  Study  of  Rock  Decomposition  Under  the  Action  of  Water,"  A.  S.  Cushman, 
Circ.  38,  Office  of  Public  Roads,  U.  S.  Dept.  Agriculture. 

"The  Development  of  the  Test  for  the  Cementing  Value  of  Road  Material." 
A.  S.  Cushman,  Proc.  Am.  Soc.  for  Test.  Mat.,  1906,  Vol.  VI,  pp.  525-531. 


INORGANIC   DUST  PREVENTIVES  41 

the  road  surface.  The  use  of  a  sprinkling  device  discharging 
the  water  through  an  adjustable  slot  so  arranged  as  to  force  it 
from  the  valves  at  an  angle  inclined  above  a  horizontal  plane 
is  one  of  the  best  methods  of  accomplishing  this.  Any  such 
device  should  always  be  under  the  control  of  the  driver,  so  that 
the  volume  of  water  discharged  may  be  easily  regulated.  The 
quantity  of  water  necessary  for  one  application  will  vary  with 
the  character  of  the  road  surface  treated,  more  being  required 
for  absorbent  surfaces  than  for  those  which  are  impervious  or 
nearly  so.  From  0.3  to  0.5  gallon  per  square  yard  may,  how- 
ever, be  taken  as  an  average.  The  frequency  of  application 
will  also  vary  according  to  local  conditions,  such  as  character  of 
the  road,  climatic  conditions,  amount  of  traffic,  etc.  In  some 
instances  it  has  been  found  necessary  to  sprinkle  a  road  as 
often  as  three  or  four  times  a  day  and  even  then  the  dust  has 
not  been  successfully  laid. 

The  cost  of  laying  dust  by  means  of  water  is  impossible  to 
estimate,  except  in  individual  cases,  being  dependent  not  only 
upon  the  quantity  required  and  frequency  of  application,  but 
also  upon  the  cost  of  the  water  itself,  price  of  labor,  efficiency 
of  labor  and  availability  of  the  water  supply.  The  last  factor 
alone  makes  it  impossible  to  water  the  average  country  road, 
which  is  not  equipped  with  the  wayside  hydrants  necessary 
to  carry  on  such  treatment. 

Aitkins  *  states  that  "The  cost  of  ordinary  sprinkling  with 
water  is  generally  about  4  s.  per  mile  of  road  eight  yards  wide. 
The  number  of  applications  varies  considerably  but  may  be  taken 
at  about  three  hundred  each  year  (two  and  one  quarter  times  each 
day  during  the  season),  at  a  cost  of  £60  per  mile  per  annum." 
This  figures  out  to  about  two  and  one-quarter  cents  per  square 
yard  per  annum.  In  the  United  States,  figures  obtained  from 
various  sources  show  that  where  any  serious  attempt  is  made  to 
keep  down  the  dust  for  a  season  by  means  of  water  sprinkling, 
this  cost  has  averaged  from  two  and  one-half  to  five  cents  per 
square  yard  per  annum.  This  represents  an  annual  expenditure 

*  "Road  Making  and  Maintenance,"  Second  Edition,  p.  328.     Griffin  and. Co. 


42  DUST   PREVENTIVES   AND   ROAD   BINDERS 

of  from  $220  to  $440  per  mile  of  fifteen  foot  roadway.  In  many 
cases  the  actual  cost  has  been  greatly  in  excess  of  the  figures 
given. 

Sea  Water.  —  It  has  long  been  known  that  certain  salts  have 
so  great  an  affinity  for  water  that  they  are  not  only  capable  of 
retaining  moisture  for  a  long  time  under  conditions  which  would 
otherwise  produce  rapid  evaporation,  but  that  they  are  capable 
of  absorbing  water  from  the  atmosphere  to  a  great  extent. 
Some  of  these  salts  are  so  hygroscopic  that  in  a  humid  atmos- 
phere they  will  often  completely  dissolve  in  the  water  which 
they  have  absorbed  from  the  air.  Salts  of  this  character  are 
termed  deliquescent,  and  it  is  to  a  great  extent  these  hygro- 
scopic and  deliquescent  salts  that  have  been  employed  as  dust 
preventives.  Their  chemical  action  upon  certain  rock  powders 
may  also  increase  the  formation  of  binding  material  to  some 
extent,  but  they  are  not  primarily  employed  for  this  purpose. 
Their  principal  use  is  to  keep  the  road  surface  in  a  semimoist 
condition  for  a  much  longer  period  than  would  be  possible  by 
the  application  of  a  corresponding  amount  of  water  only,  and 
the  number  of  sprinklings  necessary  is  therefore  greatly  reduced. 

One  of  these  salts,  magnesium  chloride  (MgCl2),  occurs  to  a 
considerable  extent  in  sea  water.  The  effect  of  its  presence  in 
the  cheaper  grades  of  table  salt  may  be  seen  in  the  tendency 
exhibited  by  the  salt  to  clump  in  damp  weather.  This  is  due 
to  the  absorption  of  water  by  the  small  amount  of  magnesium 
chloride  which  remains  even  after  the  salt  has  been  purified. 
On  account  of  the  presence  of  this  substance,  sea  water  has  been 
tried,  in  a  number  of  favorably  situated  localities,  for  the  pur- 
pose of  laying  dust.  While  the  number  of  sprinklings  has  been 
somewhat  reduced  by  this  means,  the  results  have,  as  a  rule, 
been  far  from  satisfactory,  owing  to  the  presence  of  an  excessive 
amount  of  common  salt  (sodium  chloride),  which  is  applied  at 
the  same  time  and  which  has  no  hygroscopic  properties.  In 
extremely  dry  weather,  a  hard  salty  scale  is  produced  on  the 
road  which  is  very  undesirable  and  in  wet  weather  the  mud 
contains  so  much  salt  that  it  is  injurious  to  the  varnish  and 


INORGANIC   DUST   PREVENTIVES  43 

iron  work  on  vehicles.     This  strong  salt  mud  is  also  apt  to 
cause  soreness  around  the  fetlocks  of  horses. 

Bittern.  —  In  the  process  of  manufacturing  ordinary  salt 
from  sea  water  or  other  brines,  a  waste  product  is  obtained 
which  is  known  as  bitter  brine,  or  bittern.  This  bittern  is  the 
mother  liquor  remaining  after  most  of  the  sodium  chloride  has 
been  crystallized  out  by  evaporation.  It  is  comparatively  rich 
in  magnesium  chloride,  and,  therefore,  more  suitable  for  road 
use  than  ordinary  sea  water.  It  also  contains  varying  amounts 
of  calcium  chloride,  calcium  sulphate  and  other  salts.  As  it  is 
worthless  for  other  purposes,  its  cost  is  very  low  and  in  certain 
localities  its  use  might  prove  economical.  Its  application  for 
the  purpose  of  laying  dust  is  covered  by  patent.*  So  far,  no 
very  extensive  use  has  been  made  of  this  substance,  but,  as  it 
is  apt  to  contain  a  considerable  amount  of  inert  sodium  chloride, 
the  same  objections  which  have  been  urged  against  the  use  of 
sea  water  might  be  applicable  here,  although  to  a  much  less 
extent.  It  undoubtedly  has  greater  dust-laying  qualities  than 
ordinary  sea  water,  but  not  so  much  as  the  salt  which  will 
next  be  considered,  calcium  chloride. 

Calcium  Chloride.  —  Calcium  chloride  (CaCl2)  is  one  of  the 
most  hygroscopic  and  readily  deliquescent  salts  known,  and 
should  not  be  confused  with  the  commercial  product,  commonly 
known  as  chloride  of  lime  or  bleaching  powder,  which  has  the 
formula  CaOCl2  and  is  employed  as  a  bleaching  agent  and  dis- 
infectant. From  very  concentrated  solutions  calcium  chloride 
crystallizes  with  six  molecules  of  water,  CaCl2 .  6  H20.  At  30°  C. 
these  crystals  melt  or  rather  dissolve  in  their  own  water  of  crys- 
tallization and  this  fact  makes  calcium  chloride  more  service- 
able for  dust  laying  than  magnesium  chloride.  The  latter  also 
crystallizes  with  six  molecules  of  water  and  while  in  humid  air 
such  crystals  appear  to  be  as  hygroscopic  as  the  former,  they 
are  more  stable,  and  do  not  dissolve  in  their  own  water  of  crystal- 
lization at  ordinary  temperatures.  This  means  that  under  cer- 
tain conditions  when  calcium  chloride  would  remain  in  liquid 

*  U.  S.  Patent  No.  828,643,  Aug-  * 


44 


DUST   PREVENTIVES   AND    ROAD   BINDERS 


form  upon  a  road,  magnesium  chloride  would  exist  as  a  solid  and 
would,  therefore,  be  less  efficient  as  a  dust  layer.  The  compara- 
tive water  absorbing  capacity  of  these  two  salts  in  a  humid 
atmosphere  under  normal  summer  conditions  is  shown  by  the 
following  experiment,  which  at  the  same  time  demonstrates  the 
remarkable  affinity  which  both  have  for  atmospheric  moisture. 
In  this  experiment  separate  solutions  of  the  salts  were  first 
made  and  their  actual  salt  contents  determined  by  analysis. 
Known  quantities  of  these  solutions  were  then  measured  into 
weighed  platinum  dishes  and  placed  in  a  hot  air  bath  at  95°  C. 
for  two  and  one-half  hours.  The  dishes  and  contents  were  then 
cooled  and  weighed  and  the  loss  in  weight  upon  the  basis  of 
salt  present  determined,  after  which  they  were  replaced  in  the 
oven  at  a  temperature  of  95°  C.  for  an  additional  seven  hours 
and  their  loss  in  weight  again  determined.  At  this  point  the 
contents  of  both  dishes  were  solid.  The  salts  were  next  exposed 
to  air  under  normal  conditions  for  varying  periods  and  the  per- 
centage gain  in  weight  due  to  moisture  absorbed  from  the  atmos- 
phere noted.  The  results  as  given  in  the  following  table  are 
calculated  upon  both  a  weight  and  molecular  equivalent  basis 
for  the  purpose  of  comparison. 

RELATIVE    HYGROSCOPICITY     OF    CALCIUM    AND    MAGNESIUM 

CHLORIDES. 


40  Per  cent  Solution  of  Crystals  having  6  H2O. 

Ca( 

:i2. 

Mg( 

:i2. 

Per  cent 
H2O. 

Molecules 
H20 
per  Mol. 
Salt. 

Per  cent 
H20. 

Molecules 
H20 
per  Mol. 
Salt. 

Solution  heated  for  2  \  hours  at  95°  C  

206   £ 

12  .  7 

218.0 

II.  < 

Solution  heated  for  9^  hours  at  95°  C  
Residue    exposed    to    normal    atmospheric 
conditions    24  hours 

62.2 

104.   1 

3-8 

6    2 

108.3 
138   I 

5-7 

7    3 

Residue  exposed  to  normal  atmospheric 
conditions,  48  hours  .  .  . 

144  .  3 

8.9 

168.4 

8.9 

Residue  exposed  to  normal  atmospheric 
conditions,  72  hours  

169.9 

10.  c; 

IQI  •  3 

IO.  I 

Residue  exposed  to  normal  atmospheric 
conditions,  89  hours 

108  c 

12  .  2 

2IQ.O 

ii.  6 

Residue  exposed  to  normal  atmospheric 
conditions,  96  hours  

186  « 

II  .< 

2O4  .3 

10.8 

Residue  exposed  to  normal  atmospheric 
conditions,  113  hours.  . 

184.7 

II.  4 

202.8 

10.7 

INORGANIC   DUST   PREVENTIVES  45 

From  these  figures  it  will  be  seen  that  weight  for  weight  mag- 
nesium chloride  holds  a  greater  percentage  of  water  than  calcium 
chloride,  under  the  same  conditions.  This  is  true  of  all  of  the 
results  but  it  will  be  noticed  that  at  the  point  of  maximum  absorp- 
tion one  molecule  of  calcium  chloride  is  capable  of  absorbing 
and  holding  a  greater  number  of  molecules  of  water  than  one 
molecule  of  magnesium  chloride.  The  molecular  absorption  is, 
therefore,  higher  for  the  former  and  this,  in  connection  with  the 
fact  that  at  ordinary  temperatures  CaCL  .  6  H2O  is  a  liquid 
while  MgCl2 .  6  H2O  is  a  solid,  makes  calcium  chloride  chemically 
more  efficient  as  a  dust  layer  then  magnesium  chloride. 

When  carrying  out  these  experiments  it  was  noticed  that  under 
working  conditions  the  calcium  chloride  did  not  become  solid 
until  all  but  four  molecules  of  water  were  removed  from  one 
molecule  of  CaCl2.  Magnesium  chloride,  on  the  other  hand, 
became  solid  while  still  retaining  six  molecules  of  water  to  each 
molecule  of  MgCl2.  From  the  standpoint  of  the  solid  state, 
therefore,  the  maximum  efficiency  as  shown  by  the  experiment 
would  be  as  follows,  and  these  figures  undoubtedly  represent 
more  nearly  the  relative  dust  laying  efficiency  of  the  two 
materials : 


Residue  Exposed  89  Hours. 

CaCl2  .  4  H2O. 

MgCl2  .  6  H2O. 

Per  cent  water  held  as  moisture  

80.7 

40    6 

Molecules  of  H2O  (as  moisture)  per  mol.  salt  

8.2 

5-6 

Viewed  in  this  light  solid  calcium  chloride  is  more  efficient 
than  magnesium  chloride  upon  both  a  weight  basis  and  a  molec- 
ular equivalent  basis. 

Commercial  calcium  chloride  is  obtained  for  the  most  part 
as  a  by-product  in  the  manufacture  of  soda  according  to  the 
ammonia  or  Solvay  process.  In  this  process  concentrated 
sodium  chloride  brine  is  first  saturated  with  ammonia  gas  (NH3) 
and  the  ammoniacal  brine  thus  made  treated  with  carbon  dioxide 


46  DUST   PREVENTIVES   AND   ROAD   BINDERS 

(C02).     The    resulting    reaction    which    produces    ammonium 
chloride  and  bicarbonate  of  soda  may  be  expressed  as  follows : 

NaCl  +  H2O  +  NH3  +  C02=  NH4C1  +  NaHCO3. 

The  sodium  bicarbonate  which  is  precipitated  in  this  mixture 
is  separated  by  suitable  means  and  the  mother  liquor,  containing 
ammonium  chloride,  some  undecomposed  sodium  chloride  and 
ammonium  carbonate,  is  treated  for  the  recovery  of  the  ammonia 
present,  by  distillation  with  milk  of  lime.  The  reaction  which 
produces  calcium  chloride  is  as  follows: 

2  NH4C1  +  Ca(OH)2  =  2  NH3+  CaCl2  +  2  H2O. 

Ammonia  thus  passes  off  as  a  gas  to  be  used  over  again  and 
calcium  chloride  is  left  in  solution  together  with  a  small  amount 
of  magnesium  chloride  and  any  undecomposed  sodium  chloride 
which  may  have  passed  through  the  operation.  If  the  process 
of  manufacture  is  conducted  so  as  to  transform  all  of  the  sodium 
chloride  to  carbonate,  a  solution  of  almost  pure  calcium  chloride 
will  be  obtained  as  a  by-product  and  this  solution  may  be  con- 
centrated to  any  desired  strength,  or  most  of  the  water  may  be 
removed  by  evaporation  and  the  calcium  chloride  obtained  in 
solid  form. 

Calcium  chloride  can  be  purchased  at  a  moderate  price  in  an 
almost  pure  state.  It  is  sold  either  in  solution  or  in  a  solid, 
fused  or  granular  condition.  The  solid  material  contains  about 
25  per  cent  moisture  and  75  per  cent  calcium  chloride.  This 
represents  about  two  molecules  of  H2O  per  molecule  of  CaCl2. 
In  liquid  form  it  may  be  purchased  at  any  required  dilution. 
The  ordinary  concentrated  solution  carries  about  40  per  cent 
calcium  chloride  and  has  a  specific  gravity  of  1.402.  Both  the 
solid  and  solutions  are  sold  on  a  basis  of  the  actual  calcium  chlo- 
ride content,  and  the  solid  is,  therefore,  cheaper  when  the  cost 
of  transportation  is  taken  into  account.  It  can  at  the  present 
time  be  purchased  in  this  country  at  from  $13.00  to  $16.00  per 
ton  f.o.b.,  at  points  of  manufacture.  In  England  the  same 
material  may  be  had  for  about  half  this  price,  being  sold  for 


INORGANIC   DUST   PREVENTIVES  47 

30  s.  ($7.25)  per  ton.  Because  of  this  fact,  and  also  on  account 
of  the  generally  moist  climatic  conditions  encountered  in  Eng- 
land, it  has  been  more  extensively  employed  there  than  in  this 
country. 

It  has,  however,  been  used  to  some  extent  in  the  United 
States,  and,  when  properly  applied,  has  proved  successful.  The 
amount  of  salt  and  number  of  applications  required  to  keep 
down  the  dust  satisfactorily  for  a  season  will  vary  greatly  with 
local  conditions,  but  the  exercise  of  a  little  judgment  makes  it 
possible  to  obtain  good  results  with  a  minimum  expense.  Be- 
fore considering  its  advantages  and  disadvantages,  however,  its 
method  of  application  should  be  taken  up. 

Application  of  Calcium  Chloride. — In  most  cases,  calcium  chlo- 
ride is  applied  for  the  first  time  on  the  unprepared  road,  although 
when  the  road  is  extremely  dusty  it  is  desirable  to  have  it  first 
swept.  The  solution  is  sprinkled  from  an  ordinary  watering  cart, 
so  that  on  an  average  0.4  gallon  is  applied  per  square  yard, 
although  by  regulating  the  spread  of  the  sprinkler  to  about  two- 
thirds  the  width  of  the  road,  the  middle  receives  twice  the 
amount  of  the  sides  when  the  sprinkler  passes  over  the  road 
twice.  While  the  center  receives  a  double  application  by  this 
means,  there  is  a  tendency  for  the  salt  to  become  uniformly  dis- 
tributed over  the  whole  surface,  owing  to  the  fact  that  rains 
tend  to  carry  it  to  the  sides  of  the  road.  A  15  or  20  per  cent 
solution  is  first  employed  and  at  least  two  of  these  applications 
made  in  the  first  week  or  two,  in  order  to  impregnate  the  sur- 
face thoroughly  with  the  salt. 

The  salt  thus  applied  has  a  tendency  to  retain  moisture  for 
a  considerable  length  of  time  after  an  ordinary  application  of 
water  would  have  evaporated.  On  hot  dry  days,  however,  the 
road  does  dry  out,  especially  on  portions  unprotected  by  shade, 
and  it  has  been  found  necessary  to  feed  the  salt  by  ordinary 
applications  of  water.  The  number  of  required  sprinklings  will, 
however,  be  greatly  reduced.  It  is,  of  course,  cheaper  to  feed 
the  calcium  chloride  already  on  the  road  with  water,  than  to 
apply  a  fresh  solution  each  time  the  road  becomes  dry.  In 


48  DUST   PREVENTIVES   AND    ROAD   BINDERS 

humid  weather  it  is  often  unnecessary  to  apply  water  for  days 
at  a  time,  as  the  salt  absorbs  sufficient  moisture  from  the  damp 
night  air  to  keep  the  road  in  good  condition  throughout  the 
succeeding  day. 

In  the  course  of  time,  much  of  the  calcium  chloride  is  washed 
out  of  the  road  and  has  to  be  replaced  by  fresh  material. 
Single  sprinklings  of  an  8  or  10  per  cent  solution,  applied  at 
intervals  varying  from  two  to  five  weeks  apart,  according  to 
conditions,  are  usually  sufficient  to  maintain  the  proper  amount, 
and  these  may  be  made  in  the  same  manner  as  described  for 
the  first  two.  A  too  rapid  drying  of  the  road  is  an  indication 
that  more  salt  is  needed,  and  a  little  experience  will  soon  enable 
the  overseer  or  experimenter  to  determine  just  how  often  and 
at  just  what  time  to  make  a  fresh  application.  The  same  is 
also  true  with  respect  to  feeding  the  salt  with  water. 

In  regard  to  ascertaining  and  regulating  the  strength  of  the 
solution,  the  most  convenient  method  is  to  determine  its  specific 
gravity  by  means  of  a  hydrometer.  Accurate  determinations 
have  been  made  of  the  specific  gravity  of  solutions  of  known 
percentage  composition,  and,  as  hydrometers  graduated  to 
direct  specific  gravity  readings  can  be  obtained,  the  method  is 
a  very  simple  one.  A  hydrometer  graduated  from  i  to  1.4  is 
most  suitable  for  ordinary  work,  and  by  comparing  the  readings 
with  the  following  table,  the  strength  of  solution  at  15°  C.  can  be 
immediately  ascertained.  Also  by  diluting  the  salt  or  a  con- 
centrated solution  with  water,  any  desired  strength  may  be 
obtained  if  the  dilution  is  stopped  at  the  specific  gravity  in- 
dicated for  that  particular  strength. 


Per  cent  calcium  chloride  .  .  
Specific  gravity 

i  041 

8 
i  068 

10        15 
i  086  i   132 

20 
i   181 

3° 
i  286 

40 

A  method  has  lately  been  devised  and  patented  *  for  diluting 
and  distributing  materials  miscible  with  water,  which  has  many 
advantages  as  a  time  and  labor  saver.  As  this  method  is  par- 

*  U.  S.  Patent  No.  862,939,  Aug.  13,  1907. 


INORGANIC   DUST   PREVENTIVES  49 

ticularly  applicable  to  salt  solutions,  it  may  be  well  to  describe 
it  at  this  point.  A  watering  cart  is  used  similar  to  the  ordi- 
nary type,  with  the  exception  of  a  rack  attached  to  the  rear, 
which  is  capable  of  holding  a  nest  of  five  or  six  galvanized  iron 
cans,  each  having  a  capacity  of  over  100  gallons.  The  wagon 
holds  about  600  gallons.  The  cart  is  first  loaded  with  the 
concentrated  material,  which  is  to  be  diluted.  It  is  then  driven 
to  the  first  hydrant  along  the  road.  Here,  a  sufficient  quan- 
tity of  the  material  necessary  to  give  the  desired  strength 
when  diluted  to  the  capacity  of  the  wagon  is  drawn  off  into 
one  of  the  cans.  The  wagon  then  proceeds  to  the  next  hydrant, 
where  another  lot  is  likewise  unloaded,  and  so  on.  If  the 
wagon  has  previously  been  loaded  with  a  quantity  equal  to 
some  multiple  of  the  charges  drawn  off,  a  point  will  at  last  be 
reached  where  a  quantity  equal  to  that  held  by  the  separate 
cans  remains  in  the  wagon.  Enough  water  is  then  run  in  from 
a  hydrant  to  fill  the  wagon  and  the  solution  thus  produced  is 
applied  to  the  road.  Upon  returning,  the  empty  wagon  is 
refilled  at  each  of  the  hydrants  beside  which  a  can  of  the  mate- 
rial has  been  left,  the  empty  cans  being  returned  to  the  rack. 
A  siphon  arrangement,  as  shown  in  Fig.  3,  controlled  by  the 
water  flowing  from  the  hydrant,  serves  to  lift  the  preparation 
into  the  wagon  together  with  the  water,  thus  producing  the 
desired  mixture.  By  employing  a  method  of  this  sort,  many 
unnecessary  trips  of  the  wagon  are  avoided  and  the  cost  of 
handling  is  reduced  to  a  minimum. 

Where  a  considerable  amount  of  work  is  to  be  done  with  cal- 
cium chloride,  the  concentrated  solution  may  be  prepared  or 
stored  in  large  metal  tanks  set  at  an  elevation  sufficient  to  allow 
it  to  be  run  into  the  watering  cart  by  gravity.  Some  time  is 
required  to  dissolve  the  solid  material,  and,  if  it  is  not  possible 
to  secure  a  reservoir,  the  material  should  either  be  dissolved  in 
the  watering  cart  over  night  or  else  in  the  cans,  which  should  have 
been  previously  distributed  at  the  different  hydrants. 

When  in  the  form  of  concentrated  solutions  it  should  not  be 
stored  in  wooden  casks  or  tanks,  as  its  affinity  for  water  is  so 


OF   THE 

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DUST   PREVENTIVES   AND   ROAD   BINDERS 


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INORGANIC   DUST  PREVENTIVES  $1 

great  that  the  moisture  from  the  staves  will  be  withdrawn  and 
the  shrinkage  thus  produced  is  apt  to  cause  leakage. 

While  granulated  calcium  chloride  dissolves  quite  readily  in 
water,  the  fused  product  requires  more  time.  Mechanical  agita- 
tion will  materially  assist  solution  and  should  be  employed  when 
it  is  desired  to  dissolve  the  salt  quickly.  In  cases  where  a  solu- 
tion is  made  over  night,  however,  a  good  plan  is  to  suspend  the 
material  in  a  wire  net  basket  near  the  surface  of  the  water.  By 
this  means  a  circulation  of  the  liquid  is  produced,  as  the  water 
in  contact  with  the  salt  soon  becomes  a  concentrated  solution, 
which  being  heavier  than  the  surrounding  water  sinks  to  the 
bottom  of  the  vessel  and  thus  allows  fresh  water  to  constantly 
attack  it.  If  on  the  other  hand  the  salt  is  placed  in  the  bottom 
of  the  vessel,  it  is  soon  surrounded  by  a  saturated  layer  of  water 
which  diffuses  slowly  and  greatly  retards  further  solution. 

The  principal  advantages  of  calcium  chloride  as  a  dust  layer 
are  that  it  is  odorless  and  clean.  When  present  in  sufficient 
quantity,  it  is  undoubtedly  a  good  dust  layer  if  the  atmosphere 
is  somewhat  humid,  or  if  it  is  fed  occasionally  with  water  in 
dry  weather.  While  it  is  true  that  the  formation  of  mud  in  wet 
weather  is  not  lessened,  this  mud  is  no  more  objectionable  than 
that  ordinarily  encountered,  as  not  enough  salt  is  present  to 
give  it  the  undesirable  qualities  produced  by  the  application 
of  sea  water.  In  addition,  calcium  chloride  tends  to  distribute 
the  moisture  evenly  over  the  road  surface  and  it  can  be  easily 
and  quickly  applied.  Its  use,  like  that  of  any  other  good  dust 
layer,  prolongs  the  life  of  a  road  by  retaining  the  products  of 
wear,  and,  in  some  cases,  it  may  by  chemical  action  increase  the 
cementing  value  of  the  rock  powder. 

It  has  not  to  the  author's  knowledge  been  employed  to  any 
extent  in  the  treatment  of  city  streets.  It  would,  however, 
seem  to  be  well  adapted  for  use  as  a  dust  layer  for  brick  and 
block  pavements  which  contain  crevices  where  dust  may  accu- 
mulate in  considerable  quantities.  Applied  in  solution  to  this 
type  of  pavement,  it  would  soon  find  its  way  to  the  places 
where  it  was  most  needed  and  concentrating  at  these  points 


52  DUST   PREVENTIVES   AND   ROAD   BINDERS 

should  remain  efficient  for  a  much  longer  time  than  when  applied 
to  a  macadam  road.  It  should  also  prove  of  considerable  value 
for  laying  the  dust  on  race  tracks  and  on  streets  just  before 
a  parade.  In  some  instances  it  has  been  employed  in  conjunc- 
tion with  various  other  materials  to  produce  patented  road 
preparations. 

For  macadam  treatments  its  main  disadvantage  is  that  it  is 
not  essentially  a  road  binder,  and,  at  the  end  of  a  season's  treat- 
ment, while  the  road  may  be  in  better  condition  than  at  the 
start,  no  additional  wearing  material  will  be  present  as,  for  in- 
stance, where  a  heavy  bituminous  binder  has  been  used.  Heavy 
rains  are  likely  to  wash  most  of  it  from  the  road,  and  if  a  number 
of  showers  follow  soon  after  an  application,  much  of  its  value 
will  be  lost.  Water  does  not,  however,  always  carry  away  as 
much  of  the  salt  as  might  be  supposed,  owing  to  the  peculiar 
absorbent  qualities  of  many  rock  powders.*  Another  objection 
to  its  use  is  that  in  hot  dry  weather  it  requires  feeding  with 
water  sometimes  as  often  as  once  a  day.  In  common  with  all 
other  temporary  binders  which  are  applied  in  solution  or  emul- 
sion, it  can  only  be  employed  in  localities  favored  with  a  con- 
venient water  supply. 

As  a  rule,  it  is  slightly  more  expensive  than  water  alone,  but 
when  applied  intelligently  according  to  a  system  similar  to  that 
described,  the  cost  of  treatment  is  in  some  measure  reduced. 
In  one  case,  under  severe  traffic  conditions  on  a  macadam  road, 
the  cost  of  laying  the  dust  for  one  season  was  reduced  from 
3  cents  per  square  yard  with  water  alone  to  2.7  cents  with  the  use 
of  calcium  chloride.  Six  applications  were  made,  two  in  June 
and  one  each  in  July,  August,  September  and  October,  and,  on 
very  dry  days,  the  road  was  given  one  light  sprinkling  with 
water.  By  this  treatment,  the  dust  was  successfully  laid  through- 
out the  season,  while  in  previous  seasons  four  applications  of 
water  a  day  often  proved  ineffective.  Under  certain  conditions, 
therefore,  calcium  chloride  may  not  only  prove  to  be  a  good  dust 
layer,  but  economical  as  well.  And  even  if  the  cost  is  somewhat 

*  See  "The  Effect  of  Water  on  Rock  Powders,"  loc.  cit. 


INORGANIC   DUST  PREVENTIVES  53 

greater  than  for  the  application  of  water  alone,  the  beneficial 
effects  produced  upon  the  road  will,  in  many  cases,  more  than 
compensate  this  difference. 

Examination  of  Calcium  Chloride.  —  While,  as  has  been 
stated,  commercial  calcium  chloride  or  its  solutions  may  be  ob- 
tained in  an  almost  pure  condition,  in  some  cases  it  contains 
noticeable  quantities  of  impurities  which  lower  its  efficiency  as 
a  dust  layer.  When  this  is  suspected,  a  determination  should 
be  made  of  the  actual  percentage  of  calcium  chloride  present. 
The  principal  impurities  to  be  considered  are  calcium  hydrate, 
magnesium  hydrate,  sodium  chloride  and  magnesium  chloride. 
When  dealing  with  the  solid  salt  the  presence  of  calcium  and 
magnesium  hydrates,  in  any  appreciable  quantity,  is  indicated 
by  failure  of  the  salt  to  completely  dissolve  when  treated  with 
twice  its  weight  of  water.  The  concentrated  40  per  cent  solution, 
if  clear,  never  contains  a  great  amount  of  these  substances,  owing 
to  their  slight  solubility  in  water. 

CALCIUM. 

The  actual  calcium  chloride  contents  may  be  obtained  in  the 
following  manner,  which  also  necessitates  a  determination  of 
sodium  and  magnesium  chloride  if  present.  Approximately 
i  gram  of  the  solid,  or  from  3  to  5  grams  of  the  solution  (depend- 
ing upon  its  concentration)  of  the  material  to  be  examined  is 
placed  in  a  weighing  bottle,  which  should  be  immediately 
stoppered  and  weighed.  By  subtracting  the  weight  of  the 
empty  bottle,  that  of  the  material  taken  is  ascertained.  The 
contents  of  the  bottle  should  next  be  dissolved  or  diluted  with 
water.  Any  residue  present  should  be  filtered  upon  a  9  cm. 
filter  paper  and  well  washed  with  hot  water,  in  order  to  sepa- 
rate it  from  the  soluble  material.  The  filtrate  is  then  made  up 
to  200  c.c.  and  divided  into  two  aliquot  portions,  i  and  2.  Por- 
tion number  i  is  evaporated  on  a  steam  bath  to  as  near  dryness 
as  possible,  taken  up  with  a  little  hydrochloric  acid,  diluted 
with  water  and  filtered  as  before.  This  filtrate  is  made  up 
with  water  to  200  c.c.  and  again  divided  into  two  aliquot  por- 


54  DUST  PREVENTIVES   AND   ROAD   BINDERS 

tions,  a  and  b.  Portion  a  is  made  decidedly  ammoniacal .  and 
brought  to  a  boil.  A  sufficient  quantity  of  saturated  solution 
of  ammonium  oxalate  is  then  added  to  completely  precipitate 
the  lime  and  boiling  continued  for  a  few  minutes.  After  settling, 
this  precipitate  is  collected  on  a  filter  paper  and  washed  with 
hot  water,  after  which  it  is  placed  in  a  crucible,  ignited,  cooled 
in  a  desiccator  and  weighed.  The  weight  of  the  crucible  sub- 
tracted from  this  weight  gives  the  weight  of  calcium  oxide 
found.  This  weight  multiplied  by  the  factor  0.7148  gives 
the  weight  of  calcium  (Ca)  present.  In  order  to  determine 
the  percentage  of  calcium,  it  is,  of  course,  necessary  to  mul- 
tiply this  figure  by  4  and  divide  by  the  weight  of  material 
taken. 

MAGNESIUM. 

The  filtrate  from  the  calcium  determination  is  made  slightly 
acid  with  hydrochloric  acid  and  an  excess  of  concentrated 
solution  of  disodic  phosphate  added.  It  is  then  evaporated 
to  a  bulk  not  exceeding  150  c.c.,  transferred  to  an  Erlenmeyer 
flask,  and  after  cooling  ammonia  is  added  gradually  with 
shaking  until  the  reaction  is  strongly  alkaline.  The  flask  is 
stoppered  with  a  smooth  rubber  stopper  and  shaken  vigorously 
for  five  minutes.  By  this  treatment  the  precipitate  will  usually 
be  ready  to  filter  inside  of  an  hour.  The  filtrate  should  always, 
however,  be  preserved  over  night  to  make  sure  that  no  more 
precipitate  appears.  The  precipitate  is  collected  either  on  paper 
or  a  weighed  Gooch  crucible,  burned,  blasted  and  weighed  as 
magnesium  pyrophosphate  (Mg2P2O7)  which  multiplied  by  0.2185 
equals  magnesium.  The  actual  per  cent  of  magnesium  may  be 
obtained  as  in  the  case  of  calcium. 

SODIUM. 

Portion  b  is  neutralized  with  ammonium  hydroxide,  evapo- 
rated to  dryness  and  heated  below  redness  until  the  ammonium 
salts  are  driven  off.  The  residue  is  then  dissolved  in  a  small 
amount  of  water,  and  milk  of  lime  added  in  sufficient  amount 


INORGANIC   DUST   PREVENTIVES  55 

to  precipitate  the  magnesium  if  present.  The  mixture  is  then 
boiled  for  two  or  three  minutes,  filtered  hot  and  washed  thor- 
oughly with  boiling  water.  The  lime  in  the  filtrate  is  next  pre- 
cipitated with  ammonia  and  ammonium  oxalate  and  removed 
by  nitration  in  the  same  manner  as  described  under  calcium, 
and  the  nitrate  evaporated  to  dryness  in  a  weighed  platinum 
dish.  The  residue  should  be  ignited  below  redness  until  all  am- 
monium salts  are  driven  off,  cooled  in  a  desiccator  and  weighed 
as  sodium  chloride.  This  weight  multiplied  by  0.3934  gives  the 
weight  of  sodium  found.  The  product  so  obtained,  if  multiplied 
by  4  and  divided  by  the  weight  of  material  taken,  gives  the  per- 
centage of  sodium. 

CHLORINE . 

Portion  number  2  is  made  acid  with  nitric  acid,  brought  to 
a  boil,  and  the  chlorine  present  precipitated  as  silver  chloride 
with  a  solution  of  silver  nitrate.  The  precipitate  is  then  boiled 
for  a  few  minutes  and  set  away  in  the  dark  for  a  couple  of 
hours,  after  which  it  is  quickly  filtered  upon  a  weighed  platinum 
Gooch  crucible  fitted  with  an  asbestos  pad,  ignited  to  incipient 
fusion  and  weighed.  This  weight  multiplied  by  0.2474  gives 
the  weight  of  chlorine  present,  and  the  per  cent  chlorine  may 
then  be  obtained  by  multiplying  this  product  by  2  and  dividing 
by  the  weight  of  material  taken. 

CALCULATION   OF   RESULTS. 

While  the  determinations  as  outlined  above  may  be  subject 
to  some  criticism  from  a  strictly  analytical  standpoint,  they  are 
sufficiently  accurate  for  all  practical  purposes,  and  will  give 
a  fair  estimate  of  the  amount  of  calcium  chloride  present  in 
the  original  material.  This  may  be  determined  in  the  follow- 
ing manner,  by  first  calculating  the  amount  of  chlorine  neces- 
sary to  form  chlorides  of  the  magnesium  and  sodium  present, 
subtracting  this  from  the  total  amount  of  chlorine  found  and 
calculating  the  remainder  to  calcium  chloride. 


56  DUST  PREVENTIVES  AND  ROAD   BINDERS 

Per  cent  magnesium   X  2.916  =  (i)     %  chlorine  as  MgCl2 
Per  cent  sodium  X  i . 542  =  (2)     %  chlorine  as  NaCl 

(i)  +  (2)  ~~%  chlorine  as  MgCl2  and  NaCl. 

Total  per  cent  chlorine  found.  .      % 

—  chlorine  as  MgCl2  and  NaCl.  ...     % 

=  chlorine  as  CaCl2  %~ 

Per  cent  chlorine  as  CaCl2  X  1.565  =  %  CaCl2. 

If  the  percentage  of  calcium  found  is  in  excess  of  that  required 
to  satisfy  the  chlorine,  the  presence  of  calcium  hydrate  is 
indicated.  Where  it  is  desired  to  report  the  percentage  of 
various  impurities,  the  preceding  results  can,  of  course,  be 
made  use  of  if  multiplied  by  the  proper  factors.  In  this  case 
the  residue  remaining  from  the  first  filtration  should  be  ignited 
and  weighed  as  CaO,  or  if  desired  a  complete  analysis  may  be 
made  of  it  according  to  any  of  the  well-known  methods  of  inor- 
ganic quantitative  separation  and  analysis. 

Sodium  Silicate.  —  Sodium  silicate,  commonly  known  as 
water  glass  and  having  the  formula  Na2SiO3,  has  been  employed 
to  a  slight  extent  as  a  dust  preventive  and  road  binder.  It  is 
prepared  on  a  large  scale  by  melting  together  quartz  sand  and 
sodium  carbonate  in  proper  proportions  and  also  by  melting 
together  sodium  sulphate,  quartz  sand  and  powdered  charcoal. 
Upon  exposure  to  the  air  or  to  carbonic  acid  gas  gelatinous 
silicic  acid,  which  under  certain  conditions  acts  as  an  excel- 
lent binding  material,  is  precipitated  from  its  solutions.  It 
is  extensively  employed  as  a  binding  agent  in  the  manufacture 
of  artificial  stone. 

Sodium  silicate  has  not  been  employed  as  a  road  binder  to  any 
extent  and  little  or  no  data  are  to  be  had  in  regard  to  its  value  for 
this  purpose.  It  may  be  applied  in  solution  in  the  same  general 
manner  as  calcium  chloride  and  with  some  classes  of  basic  road- 
stone,  such  as  limestone,  it  will  tend  to  cement  the  fragments 
together.  It  is  the  basis  of  a  patented  preparation  known  as 
Fitzsimons  Patent  Dust-layer,  and  has  been  employed  in  con- 
junction with  various  materials  in  other  patented  preparations. 
As  ordinarily  applied  in  weak  solutions  it  can  be  regarded  only 
as  a  semipermanent  binder,  although  it  acts  as  a  permanent 


INORGANIC   DUST  PREVENTIVES  57 

binder  when  employed  in  comparatively  large  quantities  in  the 
manufacture  of  artificial  stone.  In  the  former  case  it  is  not 
present  in  sufficient  quantity  to  produce  a  strong  bond  and  the 
thin  cementing  films  which  are  formed  are  apt  to  be  broken  under 
the  action  of  traffic,  and  when  once  broken  may  not  readily 
recement. 

Commercial  water  glass  is  not  of  definite  composition,  and 
cannot  be  obtained  crystallized.  It  may,  however,  be  obtained 
in  solution  or  in  the  solid  amorphous  state.  The  former  usually 
has  a  specific  gravity  of  about  1.38  and  may  be  purchased  in 
bulk  at  from  70  to  90  cents  per  cwt.  The  solid  sells  at  from 
$40.00  to  $45.00  per  ton. 

From  solutions  of  metallic  salts  sodium  silicate  precipitates 
insoluble  colloidal  silicates  of  the  metals.  As  these  silicates 
act  as  binding  materials,  it  would  seem  as  though  such  reactions 
might  be  made  use  of  when  treating  road  surfaces.  Thus  the 
application  of  sodium  silicate  to  a  road,  followed  by  an  applica- 
tion of  a  soluble  aluminum  or  calcium  salt,  such  as  aluminum 
sulphate  or  calcium  chloride,  has  been  suggested.  By  so  doing, 
aluminum  or  calcium  silicate,  as  the  case  may  be,  is  precipitated 
in  place  on  the  road  stone.  It  is  extremely  doubtful  if  such 
treatment  will  ever  be  extensively  employed  as  the  cost  is  apt 
to  be  high  and  the  bond  produced  by  no  means  permanent. 

Other  Salts.  —  A  number  of  other  inorganic  salts  have  also 
been  employed  as  dust  layers  and  road  binders,  most  of  them 
being  covered  by  patent.  Among  such  may  be  mentioned  a 
patented  dust  laying  preparation  known  as  Lyminite  which  is 
composed  of  sodium  nitrate,  sodium  chloride,  and  lime.  Potas- 
sium silicate  has  been  suggested  as  a  road  binder,  its  action  being 
similar  in  every  respect  to  sodium  silicate.  It  is,  however,  in 
common  with  all  potassium  compounds,  much  more  expensive 
than  the  corresponding  sodium  products  and  therefore  hot  as 
likely  to  be  used  for  road  treatment.  Certain  compounds  of  a 
mineral  base  with  an  organic  acid  have  been  employed  to  some 
extent,  but  these  materials  will  be  considered  in  the  following 
chapter  on  non-bituminous  organic  materials. 


58  DUST   PREVENTIVES   AND   ROAD   BINDERS 

Rock  Dust.  —  Many  rock  powders  under  favorable  conditions 
are  capable  of  developing  considerable  binding  or  cementing 
value.  Mention  of  this  fact  has  already  been  made  when  discuss- 
ing the  action  of  various  dust  layers,  particularly  water,  upon 
broken  stone  roads.  Certain  rock  powders  may  be  considered 
as  semipermanent  and  in  some  cases  even  as  permanent  road 
binders.  For  the  most  authoritative  and  valuable  information 
on  this  subject  reference  should  be  made  to  a  number  of  papers 
by  Page  and  Cushman.*  These  are  here  quoted  at  some  length 
as  the  facts  demonstrated  therein  have  a  most  important  bearing 
upon  the  subject  of  dust  prevention  and  road  preservation,  and, 
as  will  be  shown  later,  the  cementing  value  of  the  rock  dust 
produced  on  a  road  will  often  influence  the  selection  of  an  auxili- 
ary binder  if  such  is  needed. 

In  regard  to  the  causes  of  the  cementing  power  of  rock  pow- 
ders these  investigators  concluded  that  they  must  be  closely 
associated  with  those  which  produce  the  same  property  in  clays. 
To  quote  |  —  "The  whole  question  of  the  binding  power  of  rock 
dust  was  early  recognized  as  being  clearly  associated  with  the 
same  property  in  clays.  In  fact  considered  from  the  standpoint 
of  road  materials,  it  is  difficult  to  determine  where  the  classifi- 
cation as  clay  should  stop;  that  is  to  say,  clays  pass  impercep- 
tibly into  gravels.  Some  gravels  which  contain  a  proportion  of 
clay  base  will  be  found  to  bind,  while  a  clean  quartz  gravel 
absolutely  lacks  this  property.  While  this  is  easily  understood, 
it  does  not,  on  first  examination,  seem  to  have  any  bearing  upon 
the  great  difference  in  binding  power  which  is  exhibited  by  clean, 
deep  quarried  rock.  It  will  be  found,  however,  that  the  consid- 
erations are  identical.  Clays  themselves  are  the  product  of  rock 
decay  under  the  action  of  water  and  watery  solutions.  The 
essential  clay  base  is  supposed  to  be  a  hydrated  silicate  of  alumi- 
num, known  as  kaolin,  which  is  the  result  of  the  action  of  water 
on  the  double  silicates  of  aluminum  and  the  alkali  metals.  The 
most  typical  of  the  double  silicates  are  the  feldspars,  a  class  of 

*  Loc.  cit.,  p.  40. 

f  Bulletin  No.  85,  Bureau  of  Chemistry,  U.  S.  Dept.  of  Agriculture. 


INORGANIC   DUST  PREVENTIVES  59 

minerals  very  widely  distributed  in  nature  and  occurring  as  a 
crystalline  ingredient  of  a  great  number  of  different  rock  species. 
The  microscopical  analysis  of  rocks  shows  that  a  great  many  of 
the  minerals  which  make  up  the  aggregate  structure  have  under- 
gone secondary  changes  similar  to,  if  not  identical  with,  kaolini- 
zation  of  feldspar.  Now  kaolin,  as  found  in  nature,  although 
not  lacking  in  binding  power,  does  not,  as  a  rule,  excel  in  this 
quality.  The  ball  clays  are  usually  added  by  potters  to  the 
purer  kaolins  and  china  clays  to  increase  both  the  plasticity 
and  the  binding  power.  It  is  very  evident  that  binding 
power  is  not  due  to  the  presence  of  a  particular  mineral  such 
as  kaolinite;  on  the  contrary,  the  higher  binding  clays  show 
a  preponderance  of  amorphous  rather  than  of  crystalline 
particles. 

"The  evidence  obtained  points  to  the  following  conclusions: 
Many  minerals  under  the  action  of  water  or  of  watery  solutions 
are  decomposed.  The  secondary  products,  which  are  usually 
highly  hydrated,  may  or  may  not  lead  to  binding  power,  as  they 
are  capable  of  existing  in  allotropic  modifications  which  differ  in 
this  respect.  Alumina  and  many  other  substances  can  be  easily 
prepared  by  wet  reactions  in  the  laboratory,  either  as  gummy 
colloids  or  as  finely  crystalline  precipitates,  by  slightly  varying 
the  conditions.  In  nature  the  conditions  are  of  every  possible 
variety,  and  thus  we  find  a  physical  property  like  cementing 
power  varying  through  wide  limits  in  those  rock  species  which 
exhibit  it.  In  a  word,  those  rock  dusts  which  contain  a  certain 
proportion  of  particles  which  on  soaking  with  water  soften  to  the 
extent  that  they  become,  to  ever  so  slight  a  degree,  glue-like 
(colloid),  and  thus  adhere,  are  those  which  are  useful  to  the 
road  builder.  Many  of  the  traps,  limestones  and  sandstones,  fall 
under  this  head.  Those  rocks,  on  the  other  hand,  which  are  of 
an  entirely  unaltered  crystalline  structure,  or  those  which, 
through  metamorphic  changes  —  heat  and  pressure  —  have  had 
the  active  hydrated  particles  destroyed  —  such  as  slates  and 
quartzites  —  should  be  avoided  on  the  surface  portion  of  the 
road. 


6O  DUST   PREVENTIVES   AND   ROAD    BINDERS 

" These  conclusions  are  borne  out  in  service  where  the  problem 
has  to  be  solved  of  building  roads  of  material  which,  while  hard 
enough  to  bear  traffic,  is  without  binding  power.  A  good  ex- 
ample is  furnished  by  the  excellent  sand-clay  roads  in  the  south- 
ern states.  A  somewhat  similar  case  is  that  of  burnt-clay  roads. 
Clay  itself,  as  every  one  knows,  is  generally  too  soft  and  plastic 
to  bear  traffic  in  wet  weather,  although  its  binding  power  is 
high.  By  burning  and  clinkering  a  portion  of  the  clay  to  be  used 
on  the  road  its  hardness  is  increased  and  its  binding  power 
destroyed.  By  proper  constructive  methods  and  mixing  we 
approach  the  conditions  obtained  with  rock  dust  and  with  sand 
clay  mixtures." 

In  another  paper  by  Cushman*  on  "The  Effect  of  Water  on 
Rock  Powders,"  the  following  conclusions  are  reached:  (i) 
"When  water  comes  in  contact  with  most  rock  powders,  imme- 
diate reactions  take  place,  which  are  to  a  certain  extent  analogous 
to  those  which  take  place  with  cement  and  powdered  glass." 
(2)  "The  microscope  reveals  an  accumulation  of  amorphous 
material  of  a  gummy  appearance  largely  associated  with  the 
surfaces  of  the  crystalline  particles  as  the  action  of  water  pro- 
ceeds." (3)  "The  effect  of  wet  grinding  is  to  increase  the  bind- 
ing power  or  the  cementing  value  of  rock  powders,  and  there  are 
indications  that  the  addition  of  small  amounts  of  suitable  electro- 
lytes" (soluble  inorganic  salts,  acids,  and  bases)  "to  the  water 
will  still  further  increase  the  action." 

The  last  fact  has  a  decided  bearing  upon  the  road  binding 
value  of  the  inorganic  dust  layers  and  road  binders  already 
described  and  also  upon  the  effect  of  blending  different  road- 
stones,  one  of  which  through  being  partially  soluble  is  capable 
of  reacting  upon  the  other  to  produce  binding  films.  It  has 
been  noticed  in  cases  in  which  macadam  roads  were  being  con- 
structed of  hard  material,  such  as  granite  or  diabase,  which  are 
difficult  to  bond  under  the  roller,  that  the  surface  quickly  com- 
pacted and  gave  satisfactory  results  when  treated  with  a  top 
dressing  of  limestone  screenings.  This  observation  led  Cush- 

*  Bulletin  No.  92,  Bureau  of  Chemistry,  U.  S.  Dept.  of  Agriculture. 


INORGANIC    DUST   PREVENTIVES 


6l 


man  and  Hubbard*  to  determine  the  cementing  value  of  mix- 
tures of  these  rocks  with  limestone  as  compared  with  the  cement- 
ing values  of  the  individual  rocks.  For  this  purpose  recourse 
was  had  to  the  cementation  test  as  conducted  in  the  laboratory 
of  the  United  States  Office  of  Public  Roads,  which  will  be  de- 
scribed later.  This  work  was  conducted  during  an  investigation 
of  the  " Decomposition  of  the  Feldspars,"  granite  being  a  type  of 
feldspathic  rock.  The  results  of  a  number  of  tests  are  given 
below  and  show  conclusively  that  the  addition  of  limestone  to 
a  feldspathic  rock  increases  the  binding  power. 

RESULTS   OF   TESTS    OF   THE    CEMENTING   VALUE   OF    GRANITE 
MIXED    WITH    LIMESTONE. 


Cementing  Value. 

Granite 

.  . 

Granite. 

Limestone. 

Mixture. 

Serial  No. 

Serial  No. 

I-I3I 

I39I 

3 

27 

no 

I432 

1342 

9 

22 

56 

1435 

1335 

7 

26 

38 

1435 

1423 

7 

26 

53 

1574 

1411 

6 

20 

82 

As  the  binding  power  of  rock  dusts  is  due  to  the  decomposi- 
tion or  hydrolysis  brought  about  by  the  action  of  water,  it 
would  follow  that  if  this  binding  power  can  be  increased  by  the 
addition  of  limestone  it  is  caused  by  further  decomposition  of 
the  material,  brought  about  by  the  interaction  of  calcium  hydrox- 
ide (Ca(OH)2),  resulting  from  the  hydrolysis  of  the  limestone 
particles.  This  is  demonstrated  by  the  following  results  ob- 
tained by  determining  the  cementing  value  of  a  number  of  gran- 
ites when  treated  with  a  small  quantity  of  limewater,  or  calcium 
hydroxide  solution. 


*  Bulletin  No.  28,  Office  of  Public  Roads,  U.  S.  Department  of  Agriculture. 


62 


DUST   PREVENTIVES   AND    ROAD   BINDERS 


RESULTS   OF  TESTS   OF  THE   CEMENTING   VALUE   OF   GRANITE 
MIXED    WITH    LIMEWATER. 


Cementing    Value. 

Cementing  Value. 

Serial  No. 

Alone. 

With 
Lime  water. 

Serial  No. 

Alone. 

With 
Lime  water. 

810 

12 

21 

1276 

II 

31 

Six 

6 

16 

1329 

10 

44 

817 

II 

21 

1398 

6 

18 

893 

12 

16 

1431 

3 

19 

1008 

35 

45 

1432 

9 

12 

1192 

14 

27 

1435 

7 

15 

1275 

16 

39 

J574 

6 

II 

These  results  show  in  every  case  a  considerable  increase  in 
the  cementing  value  of  granites  so  treated  and  would  indicate 
that  the  addition  of  a  small  amount  of  lime  might  greatly  im- 
prove'the  binding  value  of  certain  roads  tones.  Of  course  the 
addition  of  a  sufficient  quantity  of  lime  would  produce  a  mortar 
in  which  the  bond  due  to  the  crystallization  of  calcium  carbonate 
will  cover  up  any  actual  increase  in  the  cementing  value  of  the 
stone  treated.  This  effect  will  also  be  produced  to  some  extent 
when  even  a  small  quantity  of  lime  is  employed,  but  results  given 
by  Lord,*  who  applied  the  principles  developed  by  Cushman  for 
rock  powders,  show  that  when  a  sample  of  chert  and  one  of 
clinker  were  so  treated  the  increase  in  cementing  value  was 
greatly  in  excess  of  that  produced  by  treating  a  chemically  inert 
slag  in  a  similar  manner.  These  results  are  given  below  and 
indicate  that  the  increase  in  cementing  value  is  due  to  the  for- 
mation of  a  hydra  ted  silicate  of  lime. 


Material. 

Mineral  Composition. 

Cementing  Value. 

Alone. 

With 
i%  CaO. 

With 
4%  CaO. 

With 
8%  CaO. 

With 
13%  CaO. 

Slag.  .  . 
Chert  .  . 
Clinker 

Olivene  and  gehlenite 
Amorphous  quartz.  .  . 
Acid  silicate  

8 
6 

4 

15 
9 
24 

33 

22 
60 

£ 

95 

2000  + 
I4OO 

*  "The  Composition  and  Properties  of  Slag  for  Road  Making."  Paper  read 
before  the  Seventh  International  Congress  of  Applied  Chemistry,  London,  1909. 


INORGANIC    DUST   PREVENTIVES 


64 


DUST   PREVENTIVES   AND    ROAD   BINDERS 


The  conclusions  to  be  drawn  from  all  of  these  tests  are  that 
mixtures  of  acid  and  basic  rocks  show  a  higher  cementing 
value  than  either  alone,  and  that  it  is  possible  by  selecting  and 
blending  certain  roadstones,  or  by  treating  the  road  with  a 
suitable  chemical  salt  or  base,  to  greatly  increase  the  natural 
bond  of  the  road  surface. 


Illustrating  Method  of  removing 
briquette 


Position  of  mold  before  Compression 
FIG.  5.     Briquette  Mold. 


Determination  of  the  Cementing  Value  of  Rock  Powders.  — 

The  cementation  test  for  rock  powders  as  conducted  by  the 
U.  S.  Office  of  Public  Roads  is  made  as  follows.     Five  hundred 


INORGANIC   DUST   PREVENTIVES  65 

grams  of  the  coarsely  crushed  rock  sample,  broken  to  pass  a 
one-half  inch  mesh,  and  90  c.c.  of  water  are  placed,  together 
with  two  steel  shot  13  cm.  in  diameter,  in  a  ball  mill.  (See 
Fig.  4.)  This  is  a  circular  cast  iron  mill,  consisting  of  two  un- 
equal segments  A  and  B  which  should  be  bolted  together  after 
the  charge  has  been  placed  inside.  It  revolves  in  a  vertical  plane 
about  the  shaft  CC,  which  bears  in  the  pillow  blocks  DD, 
and  is  driven  from  the  pulley  E  at  the  rate  of  2000  revolutions 
per  hour.  The  sample  is  ground  for  two  and  one-half  hours, 
the  action  of  the  steel  shot  reducing  the  rock  sample  to  a  stiff 
dough,  in  which  condition  it  is  ready  to  be  molded  into  briquettes. 
About  25  grams  of  this  dough  are  placed  in  a  cylindrical  metal 
die  25  mm.  in  diameter,  shown  in  Fig.  5.  A  closely  fitting  plug 
supported  by  guide  rods  is  inserted  over  the  material,  which 
is  then  molded  in  the  briquette  machine,  Fig.  6. 

In  this  machine  the  hydraulic  cylinder  A  supports  an  iron 
platform  B  through  the  piston  rod  C.  The  cylindrical  metal 
die  containing  the  material  to  be  compressed  is  placed  upon  the 
platform  and  water  admitted  to  the  cylinder  through  the 
supply  pipe  /.  As  the  piston  rises,  the  platform  and  die  are 
carried  up  with  it,  the  plug  of  the  latter  coming  in  contact 
with  a  properly  weighted  lever  arm  G.  The  weight  H  is  ad- 
justed on  the  lever  arm  so  as  to  give  a  maximum  pressure  of 
132  kilos  per  sq.  cm.  on  the  compressed  material,  which  pressure 
is  applied  only  for  an  instant.  The  total  time  of  compression 
up  to  the  maximum  is  about  30  seconds.  When  the  lever 
arm  is  raised  one-eighth  of  an  inch  it  closes  an  electric  circuit 
which  trips  a  right-angle  cock,  shutting  off  the  water  and  open- 
ing the  exhaust. 

The  briquette  is  removed  from  the  die  and  its  height  measured. 
If  it  is  not  exactly  25  mm.  the  requisite  amount  of  material  is 
added  or  subtracted  to  make  the  next  briquette  the  required 
height.  Five  briquettes  are  made  from  each  test  sample  and 
allowed  to  dry  20  hours  in  air  and  4  hours  in  a  hot  air  bath  at 
approximately  100°  C.  After  cooling  20  minutes  in  a  desiccator 
they  are  tested  by  impact  in  a  machine  especially  designed  for 


66 


DUST   PREVENTIVES  AND   ROAD   BINDERS 


INORGANIC   DUST  PREVENTIVES 


67 


FRONT 

FIG.  7.    Page  Impact  Machine. 

the  purpose  and  known  as  the  Page  Impact  Machine.  In 
this  machine  (Fig.  7)  the  motor  A  drives  the  cam  E  at  the  rate  of 
60  revolutions  per  minute,  by  means  of  a  worm  gear.  The  ham- 
mer G,  weighing  i  kg.,  is  raised  by  means  of  the  adjustable  pin  F, 
which  slides  over  the  face  of  the  cam.  With  the  one-half  kg. 
plunger  H  resting  on  the  briquette  7,  the  end  of  pin  F  is  brought 


68  DUST  PREVENTIVES  AND    ROAD   BINDERS 

in  contact  with  the  cam  as  indicated  in  the  figure,  and  the 
binding  nut  is  tightened  to  hold  the  pin  in  position.  The 
bottom  of  the  plunger  is  pressed  upon  the  briquette  by  two 
spiral  springs.  The  rise  of  the  cam  is  such  as  to  give  an  effec- 
tive drop  of  one  centimeter  to  the  hammer.  The  reaction  of 
the  briquette  after  each  blow  of  the  hammer  produces  a  vertical 
movement  in  the  end  of  the  lever  L.  This  motion  is  recorded 
on  a  sheet  of  silicated  paper  wrapped  around  the  recording 
drum  M  by  means  of  a  brass  point  at  the  end  of  lever  L. 
Each  revolution  of  the  cam  produces  a  slight  motion  of  the  drum 
so  that  the  drum  makes  a  complete  revolution  for  100  revo- 
lutions of  the  cam.  The  number  of  blows  necessary  to  destroy 
the  resilience  of  the  briquette,  so  that  no  reaction  is  recorded 
on  the  drum,  and  the  average  obtained  upon  five  briquettes  is 
taken  to  be  the  cementing  value  of  the  material.  As  compared 
with  the  results  of  service,  a  cementing  value  of  10  is  low,  20  is 
fair,  40  is  good  and  all  values  above  50  are  excellent. 

Slaking  Test  of  Rock  Powder.  Briquettes.  —  Different  rock 
powders  after  briquetting  often  behave  quite  differently  if 
allowed  to  stand  under  water.  Work  in  the  laboratory  of  the 
Office  of  Public  Roads  has  shown  that  some  will  rapidly  slake 
or  disintegrate  in  the  same  manner  that  a  lump  of  fat  clay 
slakes  under  water,  and  that  others  slake  very  slowly  or  not  at 
all.  This  property  seems  to  be  quite  independent  of  the  cement- 
ing value  of  the  rock  powder  as  ordinarily  determined,  and  as 
it  has  a  very  direct  bearing  upon  the  way  a  stone  binder  will 
behave  upon  the  road  in  rainy  weather,  should  be  determined 
before  selecting  a  roadstone.  The  test  is  made  by  placing 
the  briquette  which  has  been  molded  and  dried  in  the  man- 
ner described  under  the  cementation  test,  under  water  at 
20°  C.  and  noting  the  time  required  for  it  to  slake.  Other 
things  being  equal,  preference  should  be  given  to  rock  powders 
which  slake  slowly  or  not  at  all  over  those  which  slake 
rapidly,  for  it  is  evident  that  a  fast  slaking  rock  powder,  if 
employed  as  a  road  binder,  will  produce  a  muddy  surface  in 
wet  weather. 


INORGANIC   DUST  PREVENTIVES  69 

Slag  Powders.  —  In  the  manufacture  of  iron  and  steel, 
immense  quantities  of  slag  are  produced  in  this  country  as 
by-products.  Many  of  these  slags  are  not  unlike  certain  classes 
of  rock  in  their  physical  characteristics,  and  they  have  been 
employed  to  some  extent  as  road  materials.  In  the  paper  by 
Lord,  before  referred  to,  the  results  of  an  investigation  of  the 
cementing  value  of  slags  are  given,  and  these  results  would  seem 
to  be  of  great  interest  in  connection  with  the  selection  and  use 
of  slag  screenings  or  slag  dust  as  a  binder  for  macadam  roads. 
As  in  the  case  of  rock  powders,  it  was  found  that  the  cementing 
value  of  slag  is  caused  to  a  large  extent  by  the  hydration  of 
certain  minerals  readily  attacked  by  water,  and  that  owing  to 
variations  in  mineral  composition,  this  property  varies  greatly 
in  different  types  of  slag.  In  general  the  cementing  value  of  a 
slag  is  a  function  of  its  solubility  in  water,  and  this  fact  has  been 
made  the  basis  of  a  rapid  test  for  determining  whether  a  slag 
will  act  as  a  good  or  poor  road  binder.  As  a  rule,  those  showing 
the  highest  cementing  value  were  found  to  contain  silicate 
minerals  identical  in  crystal  form  and  chemical  composition 
with  the  active  elements,  alite  and  belite,  of  hydraulic  cements. 
The  bond  produced  in  briquettes  made  from  this  type  of  slag  is, 
therefore,  similar  to  that  produced  in  cement  and,  as  shown  in 
the  following  tables,  the  cementing  values  run  high.  The 
minerals  mentioned  are  readily  attacked  by  water,  and  those 
slags  containing  a  relatively  large  proportion  of  lime  in  solid 
solution,  therefore,  exhibit  the  highest  cementing  values.  The 
relative  solubility  of  a  slag  is  indicated  in  a  rough  way  by 
Cushman's  method  *  of  treating  a  portion  of  the  finely  ground 
powder  to  which  water  has  been  added  with  a  few  drops  of 
a  i  per  cent  alcoholic  solution  of  phenolphthalein.  When  thus 
treated,  the  more  soluble  slags  produce  a  dark  red  solution, 
the  slightly  soluble  a  faint  pink  and  the  practically  insoluble 
slags  a  colorless  solution.  The  relation  between  this  test  and 
the  cementing  value  of  the  slag  powder  as  determined  by  Lord 
is  shown  in  the  table  below. 

*  "  The  Effect  of  Water  on  Rock  Powders,"  loc.  cit. 


DUST  PREVENTIVES   AND   ROAD   BINDERS 


COLORIMETRIC  TESTS  OF  SLAG  POWDERS  WITH 
PHENOLPHTHALEIN. 


Basic  Slags. 

Intermediate  Slags. 

Acid  Slags. 

1  3 

1 

I  § 

s  . 

No. 

Color. 

e£ 

No. 

Color. 

No. 

Color. 

y 

| 

o  > 

SK 

23 

Colorless  .  .  . 

17 

8 

Faint  pink.  . 

3i 

I 

Colorless  .  .  . 

5 

25 

Colorless  .  .  . 

8 

9 

Deep  pink.  . 

24 

2 

Colorless  .  .  . 

10 

26 

Deep  red.  .  . 

!09 

12 

Faint  pink.  . 

20 

3 

Colorless  .  .  . 

3 

27 

Deep  red.  .  . 

596 

13 

Deep  pink.  . 

156 

4 

Colorless  .  .  . 

3 

28 

Deep  red.  .  . 

463 

14 

Colorless  .  .  . 

15 

6 

Colorless  .  .  . 

16 

29 

Deep  red.  .  . 

116 

15 

Deep  pink.  . 

62 

7 

Colorless  .  .  . 

ii 

As  will  be  noticed,  this  investigator  classifies  slags  under 
three  heads,  basic,  intermediate  and  acid,  and  this  classifica- 
tion is  made  according  to  their  silica  contents,  the  basic  slags 
being  comparatively  low  and  the  acid  comparatively  high  in 
silica.  Intermediate  types  are  by  far  the  most  common  and 
generally  have  a  semicrystalline  texture  and  are  light  gray  in 
color.  To  this  class  belong  most  of  the  blast  furnace  slags. 
The  cementing  value  of  these  slags  may  usually  be  greatly 
increased  by  the  addition  of  small  amounts  of  lime.  As  an 
example  of  this  fact,  Lord  cites  the  case  of  a  blast  furnace  slag 
having  an  original  cementing  value  of  15  which  was  increased 
to  200,  426,  and  2000  by  the  addition  of  i,  4  and  8  per  cent  of 
CaO  respectively.  Slags,  obtained  from  the  open  hearth  fur- 
naces, carrying  an  excess  of  lime  give  invariably  a  deep  color 
with  phenolphthalein  and  have  as  has  been  shown  excellent 
cementing  values.  They  would,  therefore,  appear  to  be  espe- 
cially adapted  for  use  as  road  binders.  Experimental  sections 
of  road  built  under  the  direction  of  the  U.  S.  Office  of  Public 
Roads  at  Youngstown,  Ohio,  during  the  summer  of  1909,  in 
which  open  hearth  slag  screenings  and  blast  furnace  slag  screen- 
ings mixed  with  5  per  cent  lime  were  employed,  have  so  far 
shown  these  materials  to  be  very  good  road  binders  as  com- 
pared with  stone  screenings. 


INORGANIC  DUST   PREVENTIVES  7 1 

It  is  very  doubtful,  however,  if  slag  will  ever  prove  to  be  an 
entirely  satisfactory  binder  for  roads  subjected  to  a  great  amount 
of  mixed  traffic,  because  of  the  rigid  nature  of  the  bond  pro- 
duced, and  the  fact  that  if  the  bond  is  once  broken  it  will  not 
form  again  except  in  the  presence  of  water.  Such  material 
may  of  course  prove  serviceable  on  roads  subjected  to  light 
traffic  and  has  the  advantage  of  being  inexpensive  in  localities 
near  which  it  is  produced.  Best  results  will  probably  be  ob- 
tained where  the  climate  is  rather  rainy  than  otherwise,  as  the 
slag  develops  its  greatest  binding  value  when  subjected  to  the 
action  of  water  for  extended  periods.  Under  these  conditions 
the  open  hearth  slag  powders  in  particular,  if  of  proper  mineral 
composition,  show  all  the  properties  of  a  slow  setting  hydraulic 
cement. 

The  use  of  slag  screenings  is  limited  to  broken  stone  roads 
and  when  employed  on  such  roads  they  should  be  applied  in 
exactly  the  same  manner  as  stone  screenings  in  macadam  road 
construction.  They  should  be  as  fine  as  possible  and  after 
being  spread  upon  the  upper  course  of  stone  should  be  thor- 
oughly puddled  with  water  and  well  rolled.  After  the  road  is 
finished  it  is  good  practice  to  close  it,  if  possible,  to  traffic  for  at 
least  a  week  and  during  that  time  to  sprinkle  it  daily  with  a 
copious  supply  of  water.  By  so  doing  the  slag  can  develop  a 
good  set  which  will  better  withstand  the  grind  of  traffic  than 
the  initial  bond  produced.  The  use  of  calcium  chloride  solu- 
tions upon  slag  bonded  roads  would  also  seem  to  be  advisable, 
as  by  this  means  moisture  is  retained  in  contact  with  the  slag 
particles  for  considerable  periods  and  a  stronger  bond  is  thus 
produced  than  if  water  alone  is  applied. 


CHAPTER  IV. 

INORGANIC   DUST  PREVENTIVES  AND   ROAD 
BINDERS. —Continued. 

Hydraulic  Cements  in  General.  —  Hydraulic  cements  are  un- 
doubtedly the  most  powerful  of  all  known  road  binders  and  in 
all  probability  will  play  an  important  part  in  the  road  of  the 
future.  As  permanent  binders  in  foundation  courses  they  can- 
not be  excelled,  but  for  road  surfaces  they  are  open  to  some 
criticism.  The  use  of  hydraulic  cements  in  road  work  has 
been  so  exhaustively  treated  in  a  number  of  textbooks  on  road 
and  pavement  construction,  that  it  seems  hardly  necessary  in 
this  book  to  discuss  the  subject  in  all  of  its  details.  As  the 
subject  of  road  binders  would,  however,  be  incomplete  without 
at  least  a  brief  description  of  their  characteristics  and  the 
methods  of  employing  them,  it  has  seemed  well  to  the  author 
to  devote  some  space  to  their  consideration. 

Hydraulic  cements  are  so  called  because  of  their  property  of 
hardening  or  setting  under  water.  They  may  be  conveniently 
divided  into  three  groups,  natural,  Portland  and  puzzolan.  The 
setting  property  of  all  of  these  cements  is  due  to  reactions  which 
take  place  when  they  are  brought  in  contact  with  water.  While 
these  reactions  are  complex  and  not  well  understood  at  the 
present  time,  they  are  known  to  be  due  to  the  presence  of  cer- 
tain minerals  which  readily  break  down  under  the  action  of 
water  and  produce  other  compounds  of  both  a  colloidal  and 
crystalline  nature,  which  interlock  and  produce  a  set.  Two  of 
these  minerals,  alite  and  belite,  which  are  found  in  Portland 
cement  have  already  been  mentioned  as  occurring  in  certain 
kinds  of  slag.  While  the  mineral  composition  of  a  cement  is 
of  course  dependent  upon  the  relative  proportion  of  the  chem- 
ical elements  present,  and  while  these  proportions  are  neces- 

72 


INORGANIC   DUST  PREVENTIVES  73 

sarily  confined  within  rather  narrow  limits,  the  fact  that  under 
varying  conditions  of  manufacture  the  elements  may  combine 
in  a  number  of  different  ways  to  form  different  classes  of  min- 
erals makes  a  chemical  analysis  of  a  cement  of  little  value  in 
determining  its  physical  properties.  Recourse  is,  therefore,  had 
to  physical  tests  for  the  purpose  of  determining  the  value  of  a 
cement  for  the  work  for  which  it  is  intended.  These  tests  will 
be  taken  up  after  briefly  considering  the  individual  types  and 
the  use  of  such  materials  in  general  as  road  binders. 

For  the  purpose  of  ascertaining  the  hydraulic  possibilities  of 
a  cement,  use  is  made  of  a  formula  for  determining  what  is 
known  as  the  Cementation  Index.  For  all  practical  purposes 
the  active  compounds  contained  in  these  cements  may  be  con- 
sidered as  tricalcic  silicate  (3  CaO  .  SiO2)  and  dicalcic  alumi- 
nate  (2  CaO  .  Si02),  although  the  subject  of  constitution  is  still 
an  open  question  and  will  not  here  be  discussed.  It  is 
customary  to  consider  magnesia  (MgO)  as  molecularly  inter- 
changeable with  lime  (CaO),  and  iron  oxide  (Fe2O3)  with  alu- 
mina (A1203).  The  cementation  index  is  the  ratio  of  silica, 
alumina  and  iron  oxide  to  lime  and  magnesia  as  expressed  with 
reference  to  their  combining  values  for  the  two  compounds 
mentioned.  In  order  that  it  may  be  employed,  it  is  of  course 
necessary  to  know  the  percentages  of  the  oxides  of  the  various 
elements  present,  and  this  can  only  be  determined  by  chemical 
analysis.  The  formula  for  the  cementation  index  may  be 
expressed  as  follows: 

Cementation  Index  = 

(2.8 X  %Si02)  +  (i.i  X  %M203)  +  (o.7  X  %Fe203) 
%CaO  +(1.4  X  %MgO) 

Except  within  certain  limits  the  chemical  analysis  and,  there- 
fore, the  cementation  index  are  of  little  value  in  determining 
the  physical  properties  of  a  cement,  unless  the  cement  has  been 
well  burned.  It  is,  however,  of  considerable  value  as  a  means 
of  classification,  as  will  appear  later.  Any  cement  with  an  index 
lower  than  i  must  contain  free  lime,  no  matter  at  how  high  a 


74  DUST   PREVENTIVES   AND    ROAD   BINDERS 

temperature  it  has  been  burned,  and  free  lime  is  known  to 
injuriously  affect  its  soundness. 

Natural  Cements.  —  Natural  cements  are  produced  by  burn- 
ing natural  argillaceous  limestones,  containing  from  15  to  40  per 
cent  silica,  alumina  and  iron  oxides,  in  a  kiln  without  previous 
mixing  and  grinding.  The  temperature  of  burning  is  about  the 
same  as  that  of  an  ordinary  limekiln.  The  resulting  product 
is  then  ground  fine,  after  which  it  exhibits  hydraulic  properties. 

Natural  cements  are  generally  yellow  to  brown  in  color  and 
run  from  2.7  to  3.1  specific  gravity.  The  cementation  index  of 
most  American  natural  cements  lies  between  1.15  and  1.60.  If 
this  index  runs  lower  than  1.15  the  cement  may  be  considered  as 
a  natural  Portland  and  if  burned  at  a  sufficiently  high  tempera- 
ture will  exhibit  much  the  same  properties  as  a  good  Portland 
cement;  otherwise  it  is  apt  to  contain  a  large  amount  of  free 
lime,  which  is  considered  detrimental.  Natural  cements  of  this 
type  should  have  a  high  specific  gravity,  that  is,  over  3.0.  As 
the  cementation  index  increases  above  1.60  the  hydraulic  proper- 
ties of  the  cement  decrease. 

According  to  standard  specifications  adopted  by  the  American 
Society  for  Testing  Materials  in  1904,  and  amended  in  1909, 
natural  cements  should  show  the  following  properties. 

NATURAL  CEMENT. 

Definition.  —  This  term  shall  be  applied  to  the  finely  pulver- 
ized product  resulting  from  the  calcination  of  an  argillaceous 
limestone  at  a  temperature  only  sufficient  to  drive  off  the  car- 
bonic acid  gas. 

SPECIFIC   GRAVITY. 

The  specific  gravity  of  the  cement  thoroughly  dried  at  100°  C. 
shall  be  not  less  than  2.8. 

FINENESS. 

It  shall  leave  by  weight  a  residue  of  not  more  than  10  per  cent 
on  the  No.  100,  and  30  per  cent  on  the  No.  200  sieve. 


INORGANIC   DUST   PREVENTIVES  75 

TIME   OF   SETTING. 

It  shall  develop  initial  set  in  not  less  than  ten  minutes,  and 
hard  set  in  not  less  than  thirty  minutes,  nor  more  than  three 
hours. 

TENSILE   STRENGTH. 

The  minimum  requirements  for  tensile  strength  for  briquettes 
one  inch  square  in  cross  section  shall  be  as  follows,  and  the  ce- 
ment shall  show  no  retrogression  in  strength  within  the  periods 
specified: 

Age.  Neat  Cement.  Strength. 

24  hours  in  moist  air 75  Ibs. 

7  days  (i  day  in  moist  air,  6  days  in  water) 150  Ibs. 

28  days  (i  day  in  moist  air,  27  days  in  water) 250  Ibs. 

One  Part  Cement,  Three  Parts  Standard  Ottawa  Sand. 

7  days  (i  day  in  moist  air,  6  days  in  water) 50  Ibs. 

28  days  (i  day  in  moist  air,  27  days  in  water) 125  Ibs. 

CONSTANCY   OF  VOLUME. 

Pats  of  neat  cement  about  three  inches  in  diameter,  one-half 
inch  thick  at  center,  and  tapering  to  a  thin  edge,  shall  be  kept 
in  moist  air  for  a  period  of  twenty-four  hours. 

(a)  A  pat  is  then  kept  in  air  at  normal  temperature. 

(b)  Another  is  kept  in  water  maintained  as  near  70°  F.  as 
practicable. 

These  pats  are  observed  at  intervals  for  at  least  twenty-eight 
days,  and,  to  satisfactorily  pass  the  tests,  should  remain  firm 
and  hard  and  show  no  signs  of  distortion,  checking,  cracking  or 
disintegration. 

Portland  Cements.  —  Portland  cements  are  produced  by  burn- 
ing to  incipient  fusion  an  intimate  artificial  mixture  of  finely 
ground  calcareous  and  argillaceous  materials,  consisting  of 
approximately  three  parts  of  calcium  carbonate  (CaCO3)  to  one 
part  of  silica,  alumina  and  iron  oxide,  and  afterwards  finely 
pulverizing  the  clinker.  This  fusion  is  usually  produced  in  a 
rotary  kiln  and  at  a  much  higher  temperature  than  that  em- 
ployed in  the  manufacture  of  natural  cements.  Portland  cement 
is  commonly  blue  to  gray  in  color  and  runs  from  3  to  3.2  specific 


76  DUST  PREVENTIVES   AND   ROAD   BINDERS 

gravity.  Its  cementation  index  should  be  between  i.o  and  1.2, 
preferably  nearer  the  first  figure  than  the  latter.  In  general 
Portland  cements  will  show  from  59  to  67  per  cent  CaO,  from  19 
to  24  per  cent  Si02  and  from  9  to  13  per  cent  A12O3  +  Fe203. 
Magnesia  to  the  extent  of  over  4  per  cent  is  regarded  as  injurious. 
According  to  standard  specifications  adopted  by  the  American 
Society  for  Testing  Materials  in  1904,  and  amended  in  1909, 
Portland  cements  should  show  the  following  properties. 

PORTLAND  CEMENTS. 

Definition.  —  This  term  is  applied  to  the  finely  pulverized 
product  resulting  from  the  calcination  to  incipient  fusion  of 
an  intimate  mixture  of  properly  proportioned  argillaceous  and 
calcareous  materials,  and  to  which  no  addition  greater  than 
3  per  cent  has  been  made  subsequent  to  calcination. 

SPECIFIC     GRAVITY. 

The  specific  gravity  of  the  cement,  thoroughly  dried  at  100°  C., 
shall  be  not  less  than  3.10.  Should  the  test  of  cement  as  re- 
ceived fall  below  this  requirement,  a  second  test  may  be  made 
upon  a  sample  ignited  at  a  low  red  heat.  The  loss  in  weight  of 
the  ignited  cement  shall  not  exceed  4  per  cent. 

FINENESS. 

It  shall  leave  by  weight  a  residue  of  not  more  than  8  per  cent 
on  the  No.  100,  and  not  more  than  25  per  cent  on  the  No.  200 
sieve. 

TIME    OF    SETTING. 

It  shall  develop  initial  set  in  not  less  than  thirty  minutes, 
but  must  develop  hard  set  in  not  less  than  one  hour,  nor  more 
than  ten  hours. 

TENSILE    STRENGTH. 

The  minimum  requirements  for  tensile  strength  for  briquettes 
one  inch  square  in  section  shall  be  as  follows,  and  the  cement 
shall  show  no  retrogression  in  strength  within  the  periods 
specified : 


INORGANIC   DUST  PREVENTIVES  77 

Age.  Neat  Cement.  Strength. 

24  hours  in  moist  air 175  Ibs. 

7  days  (i  day  in  moist  air,  6  days  in  water) 500  Ibs. 

28  days  (i  day  in  moist  air,  27  days  in  water) 600  Ibs. 

One  Part  Cement,  Three  Parts  Standard  Ottawa  Sand. 

7  days  (i  day  in  moist  air,  6  days  in  water) 200  Ibs. 

28  days  (i  day  in  moist  air,  27  days  in  water) 275  Ibs. 

CONSTANCY   OF  VOLUME. 

Pats  of  neat  cement  about  three  inches  in  diameter,  one- 
half  inch  thick  at  the  center,  and  tapering  to  a  thin  edge,  shall 
be  kept  in  moist  air  for  a  period  of  twenty-four  hours. 

(a)  A  pat  is  then  kept  in  air  at  normal  temperature  and 
observed  at  intervals  for  at  least  twenty-eight  days. 

(b)  Another  pat  is  kept  in  water  maintained  as  near  70°  F  as 
practicable,  and  observed  at  intervals  for  at  least  twenty-eight 
days. 

(c)  A  third  pat  is  exposed  in  any  convenient  way  in  an  atmos- 
phere of  steam,  above  boiling  water,  in  a  loosely  closed  vessel 
for  five  hours. 

These  pats,  to  satisfactorily  pass  the  requirements,  shall 
remain  firm  and  hard  and  show  no  signs  of  distortion,  checking, 
cracking  or  disintegrating. 

SULPHURIC  ACID  AND   MAGNESIA. 

The  cement  shall  not  contain  more  than  1.75  per  cent  of 
anhydrous  sulphuric  acid  (SO3),  nor  more  than  4  per  cent  of 
magnesia  (MgO). 

Puzzolan  Cements.  —  (Slag  cement.)  The  only  type  of 
puzzolan  cement  which  will  be  considered  is  slag  cement,  which 
is  coming  to  be  extensively  used  in  this  country.  According 
to  Eckel,*  "Slag  cement  is  composed  of  an  intimate  mechanical 
mixture  of  slaked  lime  and  granulated  blast  furnace  slag  of  suit- 
able chemical  composition,  both  materials  being  finely  pulverized 
before,  during  or  after  mixing.  The  process  of  manufacture 

*  "  Cements,  Limes  and  Plasters,"  p.  641,  Wiley  and  Sons. 


78  DUST  PREVENTIVES   AND    ROAD  BINDERS 

includes  the  granulating  and  drying  of  the  slag,  the  slaking  of  the 
lime,  the  mixing  of  the  materials,  and  the  grinding  of  the  result- 
ing cement,  together  with  every  means  which  may  be  employed 
for  the  regulation  of  the  setting  of  the  cement."  Ordinarily 
slag  cements  set  very  slowly  as  compared  with  Portland  cements 
and  small  quantities  of  caustic  soda,  potash,  sodium  chloride 
or  similar  salts  are  added  to  reduce  the  time  of  setting.  The 
color  of  these  cements  as  a  class  varies  from  light  blue  to 
lilac  and  their  specific  gravity  from  2.7  to  2.9.  From  the 
analysis  of  several  American  slag  cements,  Eckel  has  calculated 
their  cementation  index  as  being  1.59  or  over.  This  is  far  above 
the  cementation  index  of  Portland  cement,  and  is  due  to  the 
fact  that  they  contain  a  much  lower  percentage  of  lime  and 
magnesia  than  the  Portlands. 

Specifications  regarding  gravity,  fineness,  time  of  setting, 
tensile  strength  and  soundness  which  have  been  employed  in 
this  country  are  as  follows.  These  specifications  constitute  a 
part  of  the  "  Specifications  for  Puzzolan  Cement,"  published 
in  1902  by  The  Engineer  Corps,  U.  S.  Army,  and  are  given  for 
the  sake  of  comparison  with  those  for  Natural  and  Portland 
Cement,  adopted  by  the  American  Society  for  Testing  Materials. 

PUZZOLAN  CEMENT. 
SPECIFIC   GRAVITY. 

The  specific  gravity  of  the  cement,  as  determined  from  a 
sample  which  has  been  carefully  dried,  shall  be  between  2.7 
and  2.8. 

FINENESS. 

Ninety-seven  per  cent  must  pass  through  a  sieve  made  of 
No.  40  wire,  Stubb's  gauge,  having  10,000  openings  per  square 
inch. 

TIME   OF   SETTING. 

The  cement  shall  not  acquire  its  initial  set  in  less  than  forty- 
five  minutes  and  shall  acquire  its  final  set  in  ten  hours.  .  .  . 


INORGANIC   DUST   PREVENTIVES  79 

TENSILE   STRENGTH. 

Briquettes  made  of  neat  cement,  after  being  kept  in  air 
under  a  wet  cloth  for  twenty-four  hours  and  the  balance  of  the 
time  in  water,  shall  develop  tensile  strength  per  square  inch  as 
follows : 

After  seven  days,  350  pounds;  after  twenty-eight  days,  500 
pounds. 

Briquettes  made  of  one  part  cement  and  three  parts  standard 
sand  by  weight  shall  develop  tensile  strengths  per  square  inch 
as  follows  : 

After  seven  days,  140  pounds;  after  twenty-eight  days,  220 
pounds.  .  .  . 

SOUNDNESS. 

To  test  the  soundness  of  cement,  pats  of  neat  cement  mixed 
for  five  minutes  with  18  per  cent  of  water  by  weight  shall  be 
made  on  glass,  each  pat  about  three  inches  in  diameter  and 
one-half  inch  thick  at  the  center,  tapering  thence  to  a  thin  edge. 
The  pats  are  to  be  kept  under  wet  cloths  until  finally  set,  when 
they  are  to  be  placed  in  fresh  water.  They  should  not  show 
distortion  or  cracks  at  the  end  of  twenty-eight  days. 

Use  of  Cements.  —  Mixtures  of  hydraulic  cement,  sand, 
gravel  or  broken  stone  and  water  have  been  so  extensively 
employed  in  the  construction  of  cement  concrete  foundations 
for  roads  and  pavements  and  their  use  for  this  purpose  is  so 
well  understood  by  road  engineers,  that  this  phase  of  the  sub- 
ject requires  but  passing  mention.  The  correct  proportions 
of  the  various  constituents  of  such  concretes  will  of  course  vary 
with  the  character  and  size  of  the  local  material  which  will  be 
employed  as  the  mineral  aggregate.  A  good  foundation  should 
be  homogeneous,  compact,  waterproof  and  of  sufficient  strength 
to  carry  without  rupture  the  heaviest  load  to  which  the  road  is 
to  be  subjected,  and  this  can  best  be  obtained  by  the  use  of  a 
good  cement  so  proportioned  and  mixed  with  the  mineral  aggre- 
gate that  voids  are  reduced  to  a  minimum.  (For  a  method  of 
obtaining  dense  aggregates  see  page  303.)  These  points  are  dis- 


80  DUST   PREVENTIVES   AND    ROAD  BINDERS 

cussed  in  detail  in  nearly  all  books  having  to  do  with  the  con- 
struction of  roads  and  pavements.  The  concrete  may  be  mixed 
either  by  hand  or  machinery,  preferably  the  latter  on  account  of 
greater  uniformity  in  the  resulting  product.  A  modern  portable 
cement  concrete  mixing  plant  is  shown  in  Fig.  8.  The  pro- 
portions of  the  ingredients  required  should  be  determined  by 
measuring  the  percentage  of  voids  in  each  material  and  water 
should  be  added  in  quantity  just  sufficient  to  produce  a  coherent 
plastic  mass. 

According  to  Byrne,*  "The  following  are  some  of  the  more 
usual  proportions:  " 

American  hydraulic  cement i  part 

Sand 2  parts. 

Broken  stone 3  parts 

Portland  cement i  part. 

Sand 3  parts. 

Broken  stone 5  to  7  parts. 

Portland  cement i  part. 

Sand 2\  parts. 

Gravel 3  parts. 

Broken  stone 5  parts. 

The  mixed  cements  should  be  laid  and  rammed  in  layers  not 
exceeding  6  inches  in  thickness,  until  water  begins  to  ooze  out  on 
the  upper  surface.  It  should  then  be  allowed  to  set  for  at  least 
twelve  hours  without  being  disturbed  in  any  way. 

While  cement  is  admittedly  a  most  superior  binding  medium 
for  foundations  and  should  be  so  employed  when  circumstances 
permit,  its  value  as  a  binder  in  the  wearing  surface  of  a  road  is  of 
more  interest  in  connection  with  the  subject  of  this  book.  Un- 
doubtedly the  most  enduring  type  of  cement  wearing  surface  is 
cement  concrete  mixed  and  laid  in  much  the  same  manner  as 
described  for  cement  concrete  foundations.  For  such  wearing 
surfaces  Portland  cement  is  usually  to  be  preferred  to  the  other 
types.  The  latter  may,  however,  be  employed  to  advantage  in 
foundation  work.  Owing  to  their  rigidity  cement  wearing  sur- 

*  "  Highway  Construction,"  5th  Ed.,  p.  387,  Wiley  and  Sons. 


INORGANIC   DUST  PREVENTIVES 


81 


82  DUST   PREVENTIVES   AND    ROAD   BINDERS 

faces  should  be  laid  only  on  foundations  of  like  rigidity,  and  this 
necessitates  the  construction  of  an  entire  cement  concrete  pave- 
ment, which  at  the  present  time  is  entirely  too  costly  for  ordinary 
country  roads. 

One  of  the  cheapest  forms  of  concrete  road,  from  the  stand- 
point of  construction,  is  known  as  the  Hassam  Pavement,  which 
is  covered  by  patent.*  In  the  construction  of  this  road  graded 
broken  stone  of  suitable  dimensions  is  laid  and  compacted  to 
the  required  depth,  which  is  about  that  of  an  ordinary  macadam, 
and  is  then  flushed  with  a  thin  grout  of  sand  and  Portland  ce- 
ment, in  the  proportion  of  2  to  i.  By  this  means  it  is  expected 
that  the  voids  in  the  stone  aggregate  will  be  filled  to  a  great 
extent,  and  to  aid  in  forcing  the  grout  into  the  road,  rolling  and 
tamping  are  resorted  to  until  a  thin  layer  of  grout  remains  per- 
manently upon  the  surface.  A  light  course  of  pea  gravel  is  then 
spread  over  the  surface  and  well  rolled. 

Cement  concrete  roads  may  also  be  built  by  dry  mixing  graded 
stone,  sand  and  cement  in  proper  proportion.  The  dry  mixture 
is  spread  upon  the  road  and  consolidated  in  the  same  manner  as 
an  ordinary  macadam  with  the  use  of  water.  Such  roads  are, 
however,  apt  to  be  non-homogeneous,  owing  to  the  fact  that  the 
cement,  being  the  finest  ingredient,  tends  to  concentrate  at  the  bot- 
tom of  the  road,  thus  leaving  the  surface  poor  in  binding  material. 

A  good  cement  wearing  surface  has  the  advantage  of  being 
practically  waterproof,  smooth  to  any  desired  extent  according 
to  the  method  of  finishing,  easily  cleaned  and  non-absorbent  of 
heat.  It  is  well  fitted  for  automobile  traffic  alone,  but  the 
pound  of  horses'  hoofs  and  the  grind  of  heavily  loaded  steel 
tired  wheels  cause  considerable  wear  which  is  productive  of  dust. 
It  is  a  noisy  form  of  pavement,  possesses  but  little  resiliency 
and  is,  therefore,  hard  on  horses.  If  treated  with  a  thin  coat 
of  heavy  bitumen,  as  will  be  described  later,  its  undesirable 
properties  are  somewhat  modified.  Everything  considered, 
hydraulic  cements  compare  quite  favorably  with  other  kinds  of 
road  binders  and  by  some  are  thought  to  approach  the  ideal  more 
*  U.  S.  Patent  No.  851,625,  April  23,  1907. 


INORGANIC   DUST  PREVENTIVES  83 

closely  than  any  other.     The  general  trend  of  experimental  work, 
however,  seems  to  favor  the  use  of  a  bituminous  binder. 

Cement  Testing.  —  Perhaps  no  better  methods  of  cement 
testing  can  be  given  than  those  included  in  the  progress  report 
of  a  committee  appointed  by  the  American  Society  of  Civil 
Engineers  to  examine  methods  of  making  cement  tests.  This 
report,  as  made  in  1903  and  amended  in  1904,  is  presented  below: 


1.  Selection  of  Sample.  —  The  selection  of  the  sample  for  test- 
ing is  a  detail  that  must  be  left  to  the  discretion  of  the  engineer; 
the  number  and  the  quantity  to  be  taken  from  each  package 
will  depend  largely  on  the  importance  of  the  work,  the  number 
of  tests  to  be  made  and  the  facilities  for  making  them. 

2.  The  sample  shall  be  a  fair  average  of  the  contents  of  the 
package;  it  is  recommended  that,  where  conditions  permit,  one 
barrel  in  every  ten  be  sampled. 

3.  All  samples  should  be  passed  through  a  sieve  having  twenty 
meshes  per  linear  inch,  in  order  to  break  up  lumps  and  remove 
foreign  material;  this  is  also  a  very  effective  method  for  mix- 
ing  them   together  in  order  to  obtain  an  average.      For   de- 
termining  the   characteristics   of    a  shipment  of    cement,   the 
individual  samples  may  be  mixed  and  the  average  tested  ;  where 
time  will  permit,  however,  it  is   recommended   that  they   be 
tested  separately. 

4.  Method  of  Sampling.  —  Cement  in  barrels  should  be  sampled 
through  a  hole  made  in  the  center  of  one  of  the  staves,  midway 
between  the  heads,  or  in  the  head,  by  means  of  an  auger  or  a 
sampling  iron  similar  to  that  used  by  sugar  inspectors.     If  in 
bags,  it  should  be  taken  from  surface  to  center. 

CHEMICAL  ANALYSIS. 

5.  Significance.  —  Chemical    analysis    may    render    valuable 
service  in  the  detection  of   adulteration  of  cement  with  con- 
siderable amounts  of  inert  material,  such  as  slag  or  ground 
limestone.     It  is  of  use,  also,  in  determining  whether  certain 


84  DUST   PREVENTIVES  AND    ROAD    BINDERS 

constituents,  believed  to  be  harmful  when  in  excess  of  a  certain 
percentage,  as  magnesia  and  sulphuric  anhydride,  are  present 
in  inadmissible  proportions.  While  not  recommending  a  definite 
limit  for  these  impurities,  the  committee  would  suggest  that 
the  most  recent  and  reliable  evidence  appears  to  indicate  that, 
for  Portland  cement,  magnesia  to  the  amount  of  5  per  cent,  and 
sulphuric  anhydride  to  the  amount  of  1.75  per  cent,  may  safely 
be  considered  harmless. 

6.  The  determination  of  the  principal  constituents  of  cement 
—  silica,  alumina,  iron  oxide  and  lime  —  is  not  conclusive  as  an 

indication  of  quality.  Faulty  character  of  cement  results  more 
frequently  from  imperfect  preparation  of  the  raw  material  or 
defective  burning  than  from  incorrect  proportions  of  the  con- 
stituents. Cement  made  from  very  finely  ground  material,  and 
thoroughly  burned,  may  contain  much  more  lime  than  the 
amount  usually  present  'and  still  be  perfectly  sound.  On  the 
other  hand,  cements  low  in  lime  may,  on  account  of  careless 
preparation  of  the  raw  material,  be  of  dangerous  character. 
Further,  the  ash  of  the  fuel  used  in  burning  may  so  greatly 
modify  the  composition  of  the  product  as  largely  to  destroy  the 
significance  of  the  results  of  analysis. 

7.  Method.  —  As  a  method    to  be  followed  for  the  analysis 
of  cement,  that  proposed  by  the  Committee  on  Uniformity  in 
the  Analysis  of  Materials  for  the  Portland  Cement  Industry, 
of  the  New  York  Section  of  the  Society  for  Chemical  Industry, 
and  published  in  the  Journal  of  the  Society  for  January  15, 
1902,  is  recommended. 

SPECIFIC    GRAVITY. 

8.  Significance.  —  The  specific  gravity  of  cement  is  lowered 
by  underburning,   adulteration  and  hydration,   but   the  adul- 
teration must  be  in  considerable  quantity  to  affect  the  results 
appreciably. 

9.  Inasmuch  as  the  differences  in  specific  gravity  are  usually 
very  small,  great  care  must  be  exercised  in  making  the  deter- 
mination. 


INORGANIC    DUST   PREVENTIVES  8$ 

10.  When  properly  made,  this  test  affords  a  quick  check  for 
underburning  or  adulteration. 

11.  Apparatus  and  Method. — The  determination  of  specific 
gravity  is  most  conveniently  made  with  Le  Chatelier's  appa- 
ratus.    Tkis  consists  of  a  flask  Z>,  Fig.  9,  of  120  cu.  cm.  (7.32 
cu.  ins.)  capacity,  the  neck  of  which  is  about  20  cm.  (7.87  ins.) 


FIG.  9.     Le  Chatelier's  Specific  Gravity  Apparatus. 

long;  in  the  middle  of  this  neck  is  a  bulb  C,  above  and  below 
which  are  two  marks  F  and  E ;  the  volume  between  these  marks 
is  20  cu.  cm.  (1.22  cu.  ins.).  The  neck  has  a  diameter  of  about 
9  mm.  (0.35  in.),  and  is  graduated  into  tenths  of  cubic  centi- 
meters above  the  mark  F. 

12.    Benzine   (62  degrees  Baume  naphtha)  or  kerosene  free 
from  water  should  be  used  in  making  the  determination. 


86  DUST   PREVENTIVES   AND   ROAD   BINDERS 

13.  The  specific  gravity  can  be  determined  in  two  ways: 

(i)  The  flask  is  filled  with  either  of  these  liquids  to  the 
lower  mark  E,  and  64  gr.  (2.25  oz.)  of  powder,  previously  dried 
at  1 00°  C.  (2i2°F.)  and  cooled  to  the  temperature  of  the  liquid, 
are  gradually  introduced  through  the  funnel  B  (the  stem  of 
which  extends  into  the  flask  to  the  top  of  the  bulb  C),  until  the 
upper  mark  F  is  reached.  The  difference  in  weight  between 
the  cement  remaining  and  the  original  quantity  (64  gr.)  is  the 
weight  which  has  displaced  20  cu.  cm. 

14.  (2)  The  whole  quantity  of  the  powder  is  introduced, 
and  the  level  of  the  liquid  rises  to  some  division  of  the  gradu- 
ated neck.     This  reading  plus  20  cu.  cm.  is  the  volume  dis- 
placed by  64  gr.  of  the  powder. 

15.  The  specific  gravity  is  then  obtained  from  the  formula: 

0       .-    0       .,         Weight  of  Cement 

Specific  Gravity  =         °       — - — 

Displaced  Volume 

1 6.  The  flask,   during   the  operation,  is  kept  immersed  in 
water  in  a  jar  A ,  in  order  to  avoid  variations  in  the  temperature 
of  the  liquid.     The  results  should  agree  within  o.oi. 

17.  A  convenient  method  for  cleaning  the  apparatus  is  as 
follows:  The  flask  is  inverted  over  a  large  vessel,  preferably  a 
glass  jar,  and  shaken  vertically  until  the  liquid  starts  to  flow 
freely ;  it  is  then  held  still  in  a  vertical  position  until  empty ;  the 
remaining  traces  of  cement  can  be  removed  in  a  similar  manner 
by  pouring  into  the  flask  a  small  quantity  of  clean  liquid  and 
repeating  the  operation. 

1 8.  More  accurate  determinations  may  be  made  with  the 
picnometer. 

FINENESS. 

19.  Significance.  —  It  is  generally  accepted  that  the  coarser 
particles  in   cement  are  practically  inert,  and  it  is  only  the 
extremely  fine  powder  that  possesses  adhesive  or  cementing 
qualities.     The  more  finely  cement  is  pulverized,  all  other  con- 
ditions being  the  same,  the  more  sand  it  will  carry  and  produce 
a  mortar  of  a  given  strength. 


INORGANIC   DUST   PREVENTIVES  8? 

20.  The  degree  of  final  pulverization  which  the  cement  re- 
ceives at  the  place  of  manufacture  is  ascertained  by  measuring 
the  residue  retained  on  certain  sieves.     Those  known  as  the 
No.  100  and  No.  200  sieves  are  recommended  for  this  purpose. 

21.  Apparatus.  —  The  sieves  should    be  circular,   about   20 
cm.  (7.87  ins.)  in  diameter,  6  cm.  (2.36  ins.)  high,  and  provided 
with  a  pan  5  cm.  (1.97  ins.)  deep,  and  a  cover. 

22.  The  wire  cloth  should  be  woven  from  brass  wire  having 
the  following  diameters: 

No.  100,  0.0045  inch;  No.  200,  0.0024  inch. 

23.  This  cloth  should  be  mounted  on  the  frames  without 
distortion;  the  mesh  should  be  regular  in  spacing  and  be  within 
the  following  limits. 

No.  100,  96  to  100  meshes  to  the  linear  inch. 
No.  200,  1 88  to  200  meshes  to  the  linear  inch. 

24.  Fifty  grams  (1.76  oz.)  or  100  gr.   (3.52  oz.)  should  be 
used  for  the  test,  and  dried  at  a  temperature  of  100°  C.  (212°  F.) 
prior  to  sieving. 

25.  Method. — The    committee,   after   careful   investigation, 
has  reached  the  conclusion  that  mechanical  sieving  is  not  as 
practicable  or  efficient  as  hand  work,  and,  therefore,  recommends 
the  following  method: 

26.  The  thoroughly  dried  and  coarsely  screened  sample  is 
weighed  and  placed  on  the  No.  200  sieve,  which,  with  pan  and 
cover  attached,  is  held  in  one  hand  in  a  slightly  inclined  posi- 
tion,  and  moved   forward   and  backward,   at   the   same   time 
striking  the  side  gently  with  the  palm  of  the  other  hand,  at  the 
rate  of  about  200  strokes  per  minute.     The  operation  is  con- 
tinued until  not  more   than  one-tenth  of   i   per  cent  passes 
through  after  one  minute  of  continuous  sieving.     The  residue 
is  weighed,  then  placed  on  the  No.  100  sieve  and  the  operation 
repeated.     The  work  may  be  expedited  by  placing  in  the  sieve 
a  small  quantity  of  large  shot.     The  results  should  be  reported 
to  the  nearest  tenth  of  i  per  cent. 


88 


DUST   PREVENTIVES   AND    ROAD    BINDERS 


NORMAL    CONSISTENCY. 

27.  Significance.  —  The  use  of  a  proper  percentage  of  water 
in  making  the  pastes  *  from  which  pats,  tests  of  setting  and 
briquettes    are    made   is   exceedingly   important,    and    affects 
vitally  the  results  obtained. 

28.  The  determination  consists  in  measuring  the  amount  of 
water  required  to  reduce  the  cement  to  a  given  state  of  plas- 
ticity, or  to  what  is  usually  designated  the  normal  consistency. 

29.  Various  methods  have  been  proposed  for  making   this 
determination,  none  of  which  has  been  found  entirely  satis- 
factory.    The   committee  recommends  the  following: 


FIG.  10.    Vicat  Needle. 

30.  Method.  Vicat  Needle  Apparatus.  —  This  consists  of  a 
frame,  K,  Fig.  10,  bearing  a  movable  rod  L,  with  the  cap  A  at  one 
end,  and  at  the  other  the  cylinder  B,  i  cm.  (0.39  in.)  in  diameter, 
the  cap,  rod  and  cylinder  weighing  300  gr.  (10.58  oz.).  The  rod, 

*  The  term  "paste"  is  used  in  this  report  to  designate  a  mixture  of  cement  and 
water,  and  the  word  "mortar"  a  mixture  of  cement,  sand  and  water. 


INORGANIC    DUST   PREVENTIVES  89 

which  can  be  held  in  any  desired  position  by  a  screw  F,  carries 
an  indicator,  which  moves  over  a  scale  (graduated  to  centimeters) 
attached  to  the  frame  K.  The  paste  is  held  by  a  conical,  hard- 
rubber  ring  7,  7  cm.  (2.76  ins.)  in  diameter  at  the  base,  4  cm. 
(1.57  ins.)  high,  resting  on  a  glass  plate  /,  about  10  cm.  (3.94 
ins.)  square. 

31.  In  making  the  determination,  the  same  quantity  of  cement 
as  will  be  subsequently  used  for  each  batch  in  making  the  bri- 
quettes (but  not  less  than  500  grams)  is  kneaded  into  a  paste, 
as  described  in  paragraph  58,  and  quickly  formed  into  a  ball 
with  the  hands,  completing  the  operation  by  tossing  it  six  times 
from  one  hand  to  the  other,  maintained  6  ins.  apart;  the  ball  is 
then  pressed  into  the  rubber  ring,  through  the  larger  opening, 
smoothed  off,  and  placed  (on  its  large  end)  on  a  glass  plate  and 
the  smaller  end  smoothed  off  with  a  trowel;  the  paste,  confined 
in  the  ring,  resting  on  the  plate,  is  placed  under  the  rod  bearing 
the  cylinder,  which  is  brought  in  contact  with  the  surface  and 
quickly  released. 

32.  The  paste  is  of  normal  consistency  when  the  cylinder 
penetrates  to  a  point  in  the  mass  10  mm.  (0.39  in.)  below  the  top 
of  the  ring.     Great  care  must  be  taken  to  fill  the  ring  exactly 
to  the  top. 

33.  The  trial  pastes  are  made  with  varying  percentages  of 
water  until  the  correct  consistency  is  obtained. 

34.  The  committee  has   recommended,  as  normal,  a  paste, 
the  consistency  of  which  is  rather  wet,  because  it  believes  that 
variations  in  the  amount  of  compression  to  which  the  briquette 
is  subjected  in  molding  are  likely  to  be  less  with  such  a  paste. 

35.  Having  determined  in  this  manner  the  proper  percentage 
of  water  required  to  produce  a  paste  of  normal  consistency,  the 
proper  percentage  required  for  the  mortars  is  obtained  from  an 
empirical  formula. 

36.  The  committee   hopes  to  devise  such  a   formula.     The 
subject  proves  to  be  a  very  difficult  one,  and,  although  the  com- 
mittee has  given  it  much  study,  it  is  not  yet  prepared  to  make 
a  definite  recommendation. 


9o 


DUST  PREVENTIVES   AND    ROAD   BINDERS 


Note.  —  The  committee  on  Standard  Specifications  lor  cement  inserts  the 
following  table  for  temporary  use  to  be  replaced  by  one  to  be  devised  by  the  com- 
mittee of  the  American  Society  of  Civil  Engineers. 

PERCENTAGE  OF  WATER  FOR  STANDARD  MIXTURES.* 


Neat 

i-i 

1-2 

1-3 

1-4 

I- 

Neat 

i-i 

I- 

-2 

i-3 

1-4 

i-5 

18 

12  .O 

10  .0 

9.0 

8.4 

8 

.6 

33 

17.0 

I, 

3-3 

"•5 

10  .4 

9.6 

19 

12.3 

IO.2 

9.2 

8.5 

8 

.1 

34 

17-3 

It 

5.6 

11.7 

10.5 

9-7 

20 

12.7 

10.4 

9-3 

8.7 

8 

.a 

35 

17.7 

il 

j.8 

ii  .8 

10.7 

9.9 

21 

13.0 

10.7 

9-5 

8.8 

8 

•3 

36 

18.0 

i 

1.0 

12  .0 

10.8 

10  .0 

22 

13-3 

10  .9 

9-7 

8.9 

8 

-4 

37 

18.3 

i. 

1  .9 

12  .2 

10.9 

10  .1 

23 

13-7 

II  .1 

9.8 

9.1 

8 

•5 

38 

18.7 

i. 

1-4 

12.3 

II  .1 

10.2 

24 

14  .0 

11  -3 

10  .0 

9.2 

8 

.6 

39 

19  .0 

it 

1-7 

12.5 

II  .2 

10.3 

25 

14-3 

ii  .6 

10  .2 

9-3 

8 

.8 

40 

19-3 

i, 

1-9 

12.7 

ii  -3 

10  .4 

26 

14.7 

ii  .8 

10  .3 

9-5 

8 

•9 

4i 

19.7 

i 

5-1 

12.8 

ii  -5 

10.5 

27 

15.0 

12  .0 

IO-5 

9.6 

9 

.0 

42 

20  .0 

i 

5-3 

13.0 

ii.  6 

10  .6 

28 

15-3 

12  .2 

10.7 

9-7 

9 

.1 

43 

20.3 

i 

5.6 

13.2 

ix  .7 

10.7 

29 

15-7 

12.5 

10.8 

9.9 

9 

.2 

44 

20.7 

i 

5.8 

13-3 

11.9 

10.8 

3° 

16  .0 

I2.7 

II  .0 

10  .0 

9 

•3 

45 

21.0 

i 

5.o 

13-5 

12  .0 

II  .0 

31 

16.3 

12.9 

II  .2 

10  .1 

9 

•4 

46 

21.3 

i 

5.i 

13-7 

12  .1 

ii  .1 

32 

16.7 

13-1 

II  .3 

10.3 

9 

•5 

i  to 

- 

tO     2 

i  to  3 

c  to  4 

I  1 

o  s 

Cement 

^oc 

» 

•2-2-1 

2  ?O 

2OO 

I 

67 

Sand  .... 

0 

<oc 

i 

•jJO 

666 

my 

7^o 

800 

8 

27 

0 

/  j 

JO 

*  Revised  to  1909. 
TIME    OF    SETTING. 

37.  Significance.  —  The  object  of  this  test  is  to  determine  the 
time  which  elapsed  from  the  moment  water  is  added  until  the 
paste  ceases  to  be  fluid  and  plastic  (called  the  " initial  set"),  and 
also  the  time  required  for  it  to  acquire  a  certain  degree  of  hard- 
ness (called  the  "final"  or  "hard  set").     The  former  of  these 
is  the  more  important,  since,  with  the  commencement  of  setting, 
the  process  of  crystallization  or  hardening  is  said  to  begin.     As 
a  disturbance  of  this  process  may  produce  a  loss  of  strength,  it 
is  desirable  to  complete  the  operation  of  mixing  and  molding 
or  incorporating  the  mortar  into  the  work  before  the  cement 
begins  to  set. 

38.  It  is  usual  to  measure  arbitrarily  the  beginning  and  end 
of  the  setting  by  the  penetration  of  weighted  wires  of  given 
diameters. 


INORGANIC   DUST   PREVENTIVES  9 1 

39.  Method.  —  For  this  purpose  the  Vicat  Needle,  which  has 
already  been  described  in  paragraph  30,  should  be  used. 

40.  In  making  the   test,  a  paste  of  normal   consistency  is 
molded  and  placed  under  the  rod  L,  as  described  in  paragraph 
31,  this  rod,  bearing  the  cap  D  at  one  end  and  the  needle  H, 
i  mm.  (0.039  m-)  m  diameter,  at  the  other,  weighing  300  gr. 
(10.58  oz.).     The  needle  is  then  carefully  brought  in  contact 
with  the  surface  of  the  paste  and  quickly  released. 

41.  The  setting  is  said  to  have  commenced  when  the  needle 
ceases  to  pass  a  point  5  mm.  (0.20  in.)  above  the  upper  surface 
of  the  glass  plate,  and  is  said  to  have  terminated  the  moment 
the  needle  does  not  sink  visibly  into  the  mass. 

42.  The  test  pieces  should  be  stored  in  moist  air  during  the 
test;  this  is  accomplished  by  placing  them  in  a  rack  over  water 
contained  in  a  pan  and  covered  with  a  damp  cloth,  the  cloth  to 
be  kept  away  from  them  by  means  of  a  wire  screen ;  or  they  may 
be  stored  in  a  moist  box  or  closet. 

43.  Care  should  be  taken  to  keep  the  needle  clean,  as  the 
collection  of  cement  on  the  sides  of  the  needle  retards  the  pene- 
tration, while  cement  on  the  point  reduces  the  area  and  tends  to 
increase  the  penetration. 

44.  The  determination  of  the  time  of  setting  is  only  approxi- 
mate, being  materially  affected  by  the  temperature  of  the  mix- 
ing water,  the  temperature  and  humidity  of  the  air  during  the 
test,  the  percentage  of  water  used,  and  the  amount  of  molding 
the  paste  receives. 

STANDARD   SAND. 

45.  The  committee  recognizes  the  grave  objections  to  the 
standard  quartz  now  generally  used,  especially  on  account  of 
its  high  percentage  of  voids,  the  difficulty  of  compacting  in  the 
molds,  and  its  lack  of  uniformity;  it  has  spent  much  time  in 
investigating  the  various  natural  sands  which  appeared  to  be 
available  and  suitable  for  use. 

46.  For  the  present,  the  committee  recommends  the  natural 
sand  from  Ottawa,  111.,  screened  to  pass  a  sieve  having  20 


92 


DUST   PREVENTIVES   AND    ROAD   BINDERS 


meshes  per  linear  inch  and  retained  on  a  sieve  having  30  meshes 
per  linear  inch;  the  wires  to  have  diameters  of  0.0165  and 
0.0112  inch,  respectively,  i.e.,  half  the  width  of  the  opening  in 
each  case.  Sand  having  passed  the  No.  20  sieve  shall  be  con- 
sidered standard  when  not  more  than  one  per  cent  passes  a 
No.  30  sieve  after  one  minute  continuous  sifting  of  a  5oo-gram 
sample. 

47.  The  Sandusky  Portland  Cement  Company,  of  Sandusky, 
Ohio,  has  agreed  to  undertake   the  preparation  of  this  sand 
and  to  furnish  it  at  a  price  only  sufficient  to  cover  the  actual 
cost  of  preparation. 

FORM   OF   BRIQUETTE. 

48.  While   the   form   of   the   briquette   recommended   by   a 
former  committee  of   the   Society  is  not  wholly  satisfactory, 

3':- 


FIG.  ii.     Details  for  Briquette. 

this  committee  is  not  prepared  to  suggest  any  change,  other 
than  rounding  off  the  corners  by  curves  of  one-half  inch  radius, 
Fig.  ii. 


INORGANIC    DUST   PREVENTIVES  93 

MOLDS. 

49.  The   molds   should  be  made  of   brass,  bronze  or  some 
equally  non-corrodible  material,  having  sufficient  metal  in  the 
sides  to  prevent  spreading  during  molding. 

50.  Gang   molds,  which  permit  molding  a  number  of  bri- 
quettes at  one  time,  are  preferred  by  many  to  single  molds, 
since  the  greater  quantity  of  mortar  that  can  be  mixed  tends  to 
produce  greater  uniformity  in  the  results.     The  type  shown  in 
Fig.  12  is  recommended. 


FIG.  12.     Details  for  Gang  Mold. 

51.  The  molds  should  be  wiped  with  an  oily  cloth  before 
using. 

MIXING. 

52.  All  proportions  should  be  stated  by  weight;  the  quantity 
of  water  to  be  used  should  be  stated  as  a  percentage  of  the  dry 
material. 

53.  The  metric  system  is  recommended  because  of  the  con- 
venient relation  of  the  gram  and  the  cubic  centimeter. 

54.  The   temperature   of   the   room   and   the   mixing   water 
should  be  as  near  21°  C.  (70°  F.)  as  it  is  practicable  to  main- 
tan  it. 

55.  The  sand  and  cement  should  be  thoroughly  mixed  dry. 
The  mixing  should  be  done  on  some  non-absorbing  surface, 
preferably  plate  glass.     If  the  mixing  must  be  done  on  an 
absorbing  surface  it  should  be  thoroughly  dampened  prior  to 
use. 

56.  The  quantity  of  material  to  be  mixed  at  one  time  depends 
on  the  number  of  test  pieces  to  be  made;  about  1000  gr.  (35.28 
oz.)  makes  a  convenient  quantity  to  mix,  especially  by  hand 
methods. 


94  DUST  PREVENTIVES   AND   ROAD   BINDERS 

57.  The  committee,  after  investigation  of   the  various  me- 
chanical mixing  machines,  has  decided  not  to  recommend  any 
machine   that  has    thus   far  been   devised,   for   the  following 
reasons : 

(i)  The  tendency  of  most  cement  is  to  "ball  up"  in  the 
machine,  thereby  preventing  the  working  of  it  into  a  homo- 
geneous paste;  (2)  there  are  no  means  of  ascertaining  when  the 
mixing  is  complete  without  stopping  the  machine,  and  (3)  the 
difficulty  of  keeping  the  machine  clean.  «• 

58.  Method. — The  material  is  weighed  and  placed  on  the  mix- 
ing table,  and  a  crater  formed  in  the  center,  into  which  the 
proper  percentage  of  clean  water  is  poured;  the  material  on  the 
outer  edge  is  turned  into  the  crater  by  the  aid  of  a  trowel.     As 
soon  as  the  water  has  been  absorbed,  which  should  not  require 
more  than  one  minute,  the  operation  is  completed  by  vigorously 
kneading  with  the  hands  for  an  additional  one  and  one-half 
minutes,  the  process  being  similar  to  that  used  in  kneading 
dough.     A  sand-glass  affords  a  convenient  guide  for  the  time  of 
kneading.     During  the  operation  of  mixing,  the  hands  should  be 
protected  by  gloves,  preferably  of  rubber. 

MOLDING. 

59.  Having  worked  the  paste  or  mortar  to  the  proper  consist- 
ency, it  is  at  once  placed  in  the  molds  by  hand. 

60.  The  committee  has  been  unable  to  secure  satisfactory 
results  with   the  present  molding  machines;   the  operation  of 
machine  molding  is  very  slow,  and  the  present  types  permit  of 
molding  but  one  briquette  at  a  time,  and  are  not  practicable 
with  the  pastes  or  mortars  herein  recommended. 

61.  Method.  —  The    molds    should    be    filled    at    once,    the 
material  pressed  in  firmly  with  the  fingers  and  smoothed  off 
with  a  trowel  without  ramming;  the  material  should  be  heaped 
up  on  the  upper  surface  of  the  mold,  and,  in  smoothing  off,  the 
trowel  should  be  drawn  over  the  mold  in  such  a  manner  as  to 
exert  a  moderate  pressure  on  the  excess  material.     The  mold 
should  be  turned  over  and  the  operation  repeated. 


INORGANIC   DUST   PREVENTIVES  95 

62.  A  check  upon  the  uniformity  of  the  mixing  and  molding 
is  afforded  by  weighing  the  briquettes  just  prior  to  immersion 
or  upon  removal  from  the  moist  closet.     Briquettes  which  vary 
in  weight  more  than  3  per  cent  from  the  average  should  not  be 
tested. 

STORAGE   OF   THE   TEST   PIECES. 

63.  During   the   first  twenty-four  hours  after  molding   the 
test  pieces  should  be  kept  in  moist  air  to  prevent  them  from 
drying  out. 

64.  A  moist  closet  or  chamber  is  so  easily  devised  that  the 
use  of  the  damp  cloth  should  be  abandoned  if  possible.     Covering 
the  test  pieces  with  a  damp  cloth  is  objectionable,  as  commonly 
used,  because  the  cloth  may  dry  out  unequally,  and,  in  conse- 
quence, the  test  pieces  are  not  all  maintained  under  the  same 
condition.     Where  a  moist  closet  is  not  available,  a  cloth  may 
be  used  and  kept  uniformly  wet  by  immersing  the  ends  in  water. 
It  should  be  kept  from  direct  contact  with  the  test  pieces  by 
means  of  a  wire  screen  or  some  similar  arrangement. 

65.  A  moist  closet  consists  of  a  soapstone  or  slate  box,  or  a 
metal-lined  wooden  box  —  the  metal  lining  being  covered  with 
felt  and  this  felt  kept  wet.     The  bottom  of  the  box  is  so  con- 
structed  as   to  hold  water,  and  the  sides  are  provided  with 
cleats  for  holding  glass  shelves  on  which  to  place  the  briquettes. 
Care  should  be  taken  to  keep  the  air  in  the  closet  uniformly 
moist. 

66.  After  24  hours  in  moist  air  the  test  pieces  for  longer 
periods  of  time  should  be  immersed  in  water  maintained  as 
near  21°  C.  (70°  F.)  as  practicable;  they  may  be  stored  in  tanks 
or  pans,  which  should  be  of  non-corrodible  material. 

TENSILE    STRENGTH. 

67.  The  tests  may  be  made  on  any  standard  machine.     A 
solid  metal  clip,  as  shown  in  Fig.   13,  is  recommended.     This 
clip  is  to  be  used  without  cushioning  at  the  points  of  contact 
with  the  test  specimen.     The  bearing  at  each  point  of  contact 


96 


DUST   PREVENTIVES   AND   ROAD    BINDERS 


should  be  one-quarter  inch  wide,  and  the  distance  between  the 
center  of  contact  on  the  same  clip  should  be  ij  inches. 

68.  Test  pieces  should  be  broken  as 
soon  as  they  are  removed  from  the  water. 
Care  should  be  observed  in  centering 
the  briquettes  in  the  testing  machine, 
as  cross-strains,  produced  by  improper 
centering,  tend  to  lower  the  breaking 
strength.  The  load  should  not  be  ap- 
plied too  suddenly,  as  it  may  produce 
vibration,  the  shock  from  which  often 
breaks  the  briquette  before  ultimate 
strength  is  reached.  Care  must  be 
taken  that  the  clips  and  the  sides  of  the 
briquette  be  clean  and  free  from  grains 
of  sand  or  dirt,  which  would  prevent 
a  good  bearing.  The  load  should  be 
applied  at  the  rate  of  600  pounds  per 
minute.  The  average  of  the  briquettes 
of  each  sample  tested  should  be  taken 
as  the  test,  excluding  any  results  which 
are  manifestly  faulty. 


FORM  OF  CLIP 
FIG.  13. 


CONSTANCY    OF    VOLUME. 

69.  Significance.  —  The  object  is  to  develop  those  qualities 
which  tend  to  destroy  the  strength  and  durability  of  a  cement. 
As  it  is  highly  essential  to  determine  such  qualities  at  once, 
tests  of  this  character  are  for  the  most  part  made  in  a  very 
short   time,   and   are  known,   therefore,   as   accelerated   tests. 
Failure  is  revealed  by  cracking,  checking,  swelling  or  disinte- 
gration, or  all  of  these  phenomena.     A  cement  which  remains 
perfectly  sound  is  said  to  be  of  constant  volume. 

70.  Methods.  —  Tests  for    constancy  of  volume  are  divided 
into  two  classes:  (i)  normal  tests,  or  those  made  in  either  air 
or  water  maintained  at  about  21°  C.   (70°  F.),  and  (2)  accel- 
erated tests,  or  those  made  in  air,  steam  or  water  at  a  temper- 


INORGANIC   DUST   PREVENTIVES  97 

ature  of  45°  C.  (115°  F.)  and  upward.  The  test  pieces  should 
be  allowed  to  remain  24  hours  in  moist  air  before  immersion 
in  water  or  steam,  or  preservation  in  air. 

71.  For  these  tests,  pats  about  7$-  cm.  (2.95  ins.)  in  diam- 
eter, ij  cm.  (0.49  in.)  thick  at  the  center,  and  tapering  to  a  thin 
edge,  should  be  made  upon  a  clean  glass  plate  about  10  cm. 
(3.94  ins.)  square,  from  cement  paste  of  normal  consistency. 

72.  Normal  Test.  — A  pat  is  immersed  in  water  maintained 
as  near  21°  C.  (70°  F.)  as  possible  for  28  days,  and  observed  at 
intervals.     A  similar  pat  is  maintained  in  air  at  ordinary  tem- 
perature and  observed  at  intervals. 

73 .  Accelerated  Test.  —  A  pat  is  exposed  in  any  convenient 
way  in  an  atmosphere  of  steam,  above  boiling  water,  in  a  loosely 
closed  vessel,  for  three  hours. 

74.  To  pass  these  tests  satisfactorily,  the  pats  should  remain 
firm  and  hard,  and  show  no  signs  of  cracking,  distortion  or 
disintegration. 

75.  Should  the  pat  leave  the  plate,  distortion  may  be  de- 
tected best  with  a  straightedge  applied  to  the  surface  which 
was  in  contact  with  the  plate. 

76.  In  the  present  state  of  our  knowledge  it  cannot  be  said 
that  cement  should  necessarily  be  condemned  simply  for  fail- 
ure to  pass  the  accelerated  tests;  nor  can  a  cement  be  consid- 
ered entirely  satisfactory,  simply  because  it  has  passed  these 
tests. 

Analysis  of  Cements.  —  The  following  methods  of  analysis 
have  been  suggested  by  a  committee  of  the  New  York  section, 
Society  of  Chemical  Industry,  consisting  of  W.  F.  Hillebrand 
and  Clifford  Richardson.  For  accurate  work  these  methods 
should  be  closely  followed: 

SOLUTION. 

One-half  gram  of  the  finely  powdered  substance  is  to  be 
weighed  out  and,  if  a  limestone  or  unburned  mixture,  strongly 
ignited  in  a  covered  platinum  crucible  over  a  strong  blast  for 
15  minutes,  or  longer  if  the  blast  is  not  powerful  enough  to 


98  DUST  PREVENTIVES  AND   ROAD  BINDERS 

effect  complete  conversion  to  a  cement  in  this  time.  It  is 
then  transferred  to  an  evaporating  dish,  preferably  of  platinum 
for  the  sake  of  celerity  in  evaporation,  moistened  with  enough 
water  to  prevent  lumping,  and  5  to  10  c.c.  of  strong  HC1  added, 
and  digested  with  the  aid  of  gentle  heat  and  agitation  until  solu- 
tion is  complete.  Solution  may  be  aided  by  light  pressure 
with  the  flattened  end  of  a  glass  rod.*  The  solution  is  then 
evaporated  to  dryness,  as  far  as  this  may  be  possible  on  the 
bath. 

SILICA  (SiO2). 

The  residue  without  further  heating  is  treated  at  first  with 
5  to  10  c.c.  of  strong  HC1,  which  is  then  diluted  to  half  strength 
or  less,  or  upon  the  residue  may  be  poured  at  once  a  larger 
volume  of  acid  of  half  strength.  The  dish  is  then  covered  and 
digestion  allowed  to  go  on  for  ten  minutes  on  the  bath,  after 
which  the  solution  is  filtered  and  the  separated  silica  washed 
thoroughly  with  water.  The  filtrate  is  again  evaporated  to 
dryness,  the  residue  without  further  heating  taken  up  with 
acid  and  water  and  the  small  amount  of  silica  it  contains  sep- 
arated on  another  filter  paper.  The  papers  containing  the  res- 
idue are  transferred  wet  to  a  weighed  platinum  crucible,  dried, 
ignited,  first  over  a  Bunsen  burner  until  the  carbon  of  the 
filter  is  completely  consumed,  and  finally  over  the  blast  for 
fifteen  minutes  and  checked  by  a  further  blasting  for  ten  min- 
utes or  to  constant  weight.  The  silica,  if  great  accuracy  is 
desired,  is  treated  in  the  crucible  with  about  10  c.c.  of  HF1 
and  four  drops  of  H2SO4  and  evaporated  over  a  low  flame  to 
complete  dryness.  The  small  residue  is  finally  blasted,  for  a 
minute  or  two,  cooled  and  weighed.  The  difference  between 
this  weight  and  the  weight  previously  obtained  gives  the  amount 
of  silica. f 

*  If  anything  remains  undecomposed  it  should  be  separated,  fused  with  a  little 
Na2CO3,  dissolved  and  added  to  the  original  solution.  Of  course  a  small  amount 
of  separated  non-gelatinous  silica  is  not  to  be  mistaken  for  undecomposed  matter. 

t  For  ordinary  controf  in  the  plant  laboratory  this  correction  may,  perhaps, 
be  neglected;  the  double  evaporation  never. 


INORGANIC   DUST  PREVENTIVES  99 

ALUMINA  AND  IRON  (A12O3  and  Fe2O3). 
The  filtrate,  about  250  c.c.,  from  the  second  evaporation 
for  SiO2  is  made  alkaline  with  NH4OH  after  adding  HC1,  if  need 
be,  to  insure  a  total  of  10  to  15  c.c.  strong  acid,  and  boiled  to 
expel  excess  of  NH3,  or  until  there  is  but  a  faint  odor  of  it,  and 
the  precipitated  iron  and  aluminum  hydrates,  after  settling,  are 
washed  once  by  decantation  and  slightly  on  the  filter.  Setting 
aside  the  filtrate,  the  precipitate  is  dissolved  in  hot  dilute  HC1, 
the  solution  passing  into  the  beaker  in  which  the  precipitation 
was  made.  The  aluminum  and  iron  are  then  reprecipitated  by 
NH4OH,  boiled  and  the  second  precipitate  collected  and  washed 
on  the  same  filter  used  in  the  first  instance.  The  filter  paper,, 
with  the  precipitate,  is  then  placed  in  a  weighed  platinum  cru- 
cible, the  paper  burned  off  and  the  precipitate  ignited  and  finally 
blasted  five  minutes,  with  care  to  prevent  reduction,  cooled  and 
weighed  as  A12O3  +  Fe2O3*. 

IRON  (Fe2O3). 

The  combined  iron  and  aluminum  oxides  are  fused  in  a  plati- 
num crucible  at  a  very  low  temperature  with  about  3  to  4  grams 
of  KHSO4,  or,  better,  NaHSO4,  the  melt  taken  up  with  so  much 
dilute  H2SO4  that  there  shall  be  no  less  than  5  grams  absolute 
acid  and  enough  water  to  effect  solution  on  heating.  The  solu- 
tion is  then  evaporated  and  eventually  heated  till  acid  fumes 
come  off  copiously.  After  cooling  and  redissolving  in  water  the 
small  amount  of  silica  is  filtered  out,  weighed  and  corrected  by 
HF1  and  H2SO4.|  The  filtrate  is  reduced  by  zinc,  or  preferably 
by  hydrogen  sulphide,  boiling  out  the  excess  of  the  latter  after- 
wards while  passing  CO2  through  the  flask,  and  titrated  with 
permanganate.J  The  strength  of  the  permanganate  solution 
should  not  be  greater  than  .0040  gr.  Fe2O3  per  c.c. 

*  This   precipitate   contains  TiO2,  P2O5,  Mn3O4. 

t  This  correction  of  A12O3  +  Fe2O3  for  silica  should  not  be  made  when  the  HF1 
correction  of  the  main  silica  has  been  omitted,  unless  that  silica  was  obtained  by 
only  one  evaporation  and  nitration.  After  two  evaporations  and  filtrations  i  to  2 
mg.  of  SiO2  are  still  to  be  found  with  the  A12O3  +  Fe2O3. 

t  In  this  way  only  is  the  influence  of  titanium  to  be  avoided  and  a  correct 
result  obtained  for  iron. 


IOO  DUST  PREVENTIVES   AND   ROAD    BINDERS 

LIME    (CaO). 

To  the  combined  filtrate  from  the  A12O3  +  Fe2O3  precipitate  a 
few  drops  of  NH4OH  are  added,  and  the  solution  brought  to  boil- 
ing. To  the  boiling  solution  20  c.c.  of  a  saturated  solution 
of  ammonium  oxalate  are  added,  and  the  boiling  continued  until 
the  precipitated  CaC2O4  assumes  a  well-defined  granular  form. 
It  is  then  allowed  to  stand  for  twenty  minutes,  or  until  the 
precipitate  has  settled,  and  then  filtered  and  washed.  The 
precipitate  and  filter  are  placed  wet  in  a  platinum  crucible,  and 
the  paper  burned  off  over  a  small  flame  of  a  Bunsen  burner.  It 
is  then  ignited,  redissolved  in  HC1,  and  the  solution  made  up  to 
100  c.c.  with  water.  Ammonia  is  added  in  slight  excess,  and  the 
liquid  is  boiled.  If  a  small  amount  of  A12O3  separates  this  is 
filtered  out,  weighed,  and  the  amount  added  to  that  found  in 
the  first  determination,  when  greater  accuracy  is  desired.  The 
lime  is  then  reprecipitated  by  ammonium  oxalate,  allowed  to 
stand  until  settled,  filtered,  and  washed,*  weighed  as  oxide  by 
ignition  and  blasting  in  a  covered  crucible  to  constant  weight, 
or  determined  with  dilute  standard  permanganate.! 

MAGNESIA    (MgO). 

The  combined  filtrates  from  the  calcium  precipitates  are  acidi- 
fied with  HC1  and  concentrated  on  the  steam  bath  to  about 
150  c.c.,  10  c.c.  of  saturated  solution  of  Na(NH4)HPO4  are  added, 
and  the  solution  boiled  for  several  minutes.  It  is  then  removed 
from  the  flame  and  cooled  by  placing  the  beaker  in  ice  water. 
After  cooling,  NH4OH  is  added  drop  by  drop  with  constant  stir- 
ring until  the  crystalline  ammonium-magnesium  orthophosphate 
begins  to  form,  and  then  in  moderate  excess,  the  stirring  being 
continued  for  several  minutes.  It  is  then  set  aside  for  several 
hours  in  a  cool  atmosphere  and  filtered.  The  precipitate  is  re- 
dissolved  in  hot  dilute  HC1,  the  solution  made  up  to  about 
loo  c.c.,  i  c.c.  of  a  saturated  solution  of  Na(NH4)HPO4  added, 

*  The  volume  of  wash-water  should  not  be  too  large;  vide  Hillebrand. 
f  The  accuracy  of  this  method  admits  of  criticism,  but  its  convenience  and 
rapidity  demand  its  insertion. 


INORGANIC   DUST   PREVENTIVES  IOI 

and  ammonia  drop  by  drop,  with  constant  stirring  until  the 
precipitate  is  again  formed  as  described  and  the  ammonia  is  in 
moderate  excess.  It  is  then  allowed  to  stand  for  about  two 
hours,  when  it  is  filtered  on  a  paper  or  a  Gooch  crucible,  ignited, 
cooled  and  weighed  as  Mg2P2O7. 

ALKALIES  (K2O  and  Na2O). 

For  the  determination  of  the  alkalies,  the  well-known  method 
of  Prof.  J.  Lawrence  Smith  is  to  be  followed,  either  with  or 
without  the  addition  of  CaCO3  with  NH4C1. 

ANHYDROUS   SULPHURIC   ACID    (S03). 

One  gram  of  the  substance  is  dissolved  in  15  c.c.  of  HC1,  fil- 
tered and  the  residue  washed  thoroughly.* 

The  solution  is  made  up  to  250  c.c.  in  a  beaker  and  boiled. 
To  the  boiling  solution  10  c.c.  of  a  saturated  solution  of  BaCl2 
are  added  slowly  drop  by  drop  from  a  pipette  and  the  boiling 
continued  until  the  precipitate  is  well  formed,  or  digestion  on 
the  steam  bath  may  be  substituted  for  the  boiling.  It  is  then  set 
aside  over  night,  or  for  a  few  hours,  filtered,  ignited  and  weighed 
as  BaS04. 

TOTAL   SULPHUR. 

One  gram  of  the  material  is  weighed  out  in  a  large  platinum 
crucible  and  fused  with  Na2CO3  and  a  little  KNOa,  being  careful 
to  avoid  contamination  from  sulphur  in  the  gases  from  source  of 
heat.  This  may  be  done  by  fitting  the  crucible  in  a  hole  in  an 
asbestos  board.  The  melt  is  treated  in  the  crucible  with  boil- 
ing water  and  the  liquid  poured  into  a  tall  narrow  beaker  and 
more  hot  water  added  until  the  mass  is  disintegrated.  The 
solution  is  then  filtered.  The  filtrate  contained  in  a  No.  4  beaker 
is  to  be  acidulated  with  HC1  and  made  up  to  250  c.c.  with  dis- 
tilled water,  boiled,  the  sulphur  precipitated  as  BaSO4  and 
allowed  to  stand  over  night  or  for  a  few  hours. 

*  Evaporation  to  dryness  is  unnecessary,  unless  gelatinous  silica  should  have 
separated,  and  should  never  be  performed  on  a  bath  heated  by  gas;  vide  Hille- 
brand. 


102  DUST  PREVENTIVES   AND   ROAD   BINDERS 

LOSS   ON  IGNITION. 

Half  a  gram  of  cement  is  to  be  weighed  out  in  a  platinum 
crucible,  placed  in  a  hole  in  an  asbestos  board  so  that  about 
three-fifths  of  the  crucible  projects  below,  and  blasted  fifteen 
minutes,  preferably  with  an  inclined  flame.  The  loss  by  weight, 
which  is  checked  by  a  second  blasting  of  five  minutes,  is  the  loss 
on  ignition. 

May,  1903:  Recent  investigations  have  shown  that  large 
errors  in  results  are  often  due  to  the  use  of  impure  distilled  water 
and  reagents.  The  analyst  should,  therefore,  test  his  distilled 
water  by  evaporation  and  his  reagents  by  appropriate  tests 
before  proceeding  with  his  work. 

Summary  and  Conclusions.  —  In  Chapters  III  and  IV  the 
inorganic  dust  layers  and  road  binders  have  been  considered  in 
some  detail,  both  as  regards  their  chemical  and  physical  charac- 
teristics, methods  of  application  and  examination.  The  mate- 
rials have  been  discussed  in  the  order  of  their  binding  value 
from  water  alone,  the  poorest,  to  Portland  cement,  the  most 
powerful  binder.  A  significant  fact  to  be  noted  is  that  all  of  these 
materials  are  dependent  for  their  binding  value  upon  the  pres- 
ence or  action  of  water.  In  the  former  case  water  produces  a 
weak  physical  bond,  but  in  the  latter  often  a  very  powerful 
chemical  bond  due  to  the  formation  of  hydra  ted  compounds. 
Certain  salts  such  as  sodium  silicate  and  bases  such  as  quick- 
lime may  increase  the  action  of  water  upon  road  materials,  but 
they  are  inert  if  water  is  not  present.  The  position  of  stone 
screenings,  rock  dust  and  clays  is  shown  to  be  among  the  semi- 
permanent binders  and  the  action  of  water  upon  the  two  former 
somewhat  analogous  to  its  action  upon  hydraulic  cements.  A 
connecting  link  between  the  two  would  seem  to  exist  in  the 
reactions  which  take  place  between  water  and  certain  kinds  of 
slag  powders.  The  advantages  of  employing  hydraulic  cements 
as  binders  for  foundation  courses  have  been  particularly  empha- 
sized and  their  suitability  for  wearing  surfaces  discussed. 


CHAPTER  V. 

ORGANIC  NON-BITUMINOUS  DUST  PREVENTIVES  AND  ROAD 

BINDERS. 

ORGANIC  non-bituminous  materials  constitute  the  least  impor- 
tant class  of  dust  preventives  and  road  binders.  They  have  for  the 
most  part  been  employed  to  a  very  limited  extent  except  perhaps 
in  patented  preparations  in  combination  with  other  materials  of 
varying  character.  In  general  they  may  be  said  to  include  cer- 
tain vegetable  and  animal  oils  of  little  value,  other  than  as  dust 
layers;  waste  products  from  such  sources  as  wood  pulp  mills  and 
sugar  refineries,  which  may  be  considered  as  semipermanent 
binders;  and  compounds  of  rosin  or  resinic  acids  with  inorganic 
bases,  which  are  perhaps  more  lasting  in  their  effect  and  may  be 
considered  as  permanent  binders.  Most  of  these  materials  have 
been  employed  in  only  a  few  isolated  experiments  so  that  but 
little  reliable  data  are  to  be  had  as  to  the  best  method  of  applying 
them,  and  their  comparative  value  as  binders  under  varying  con- 
ditions. Their  use  has  ordinarily  been  confined  to  localities  near 
which  they  are  produced,  although  the  fact  that  some  of  them  are 
waste  products,  and  therefore  cheap,  should  place  them  in  com- 
petition with  the  other  classes  of  materials  in  certain  instances, 
and  widen  their  sphere  of  usefulness. 

Vegetable  Oils.  —  Vegetable  oils  as  a  class  can  only  be  con- 
sidered as  dust  layers  and  temporary  binders,  as  they  contain 
little  or  no  true  binding  base,  but  are  dependent  upon  their 
moistening  or  oiling  effect  to  hold  the  dust  particles  together. 
Their  action  is,  in  this  respect,  precisely  the  same  as  that  of  water, 
but  the  results  are  of  a  more  lasting  character  as  the  oils  are 
less  volatile  than  water,  and,  therfore,  remain  upon  the  road  for 
a  longer  time  and  prove  effective  until  they  have  become  satu- 
rated with  dust.  Their  binding  value  or  lack  of  binding  value 

103 


IO4  DUST   PREVENTIVES   AND   ROAD   BINDERS 

may  be  readily  demonstrated  by  making  up  rock  dust  briquettes 
in  which  the  oil  is  substituted  for  water  and  subjecting  them  to 
the  cementation  test  described  on  page  64.  As  a  typical  ex- 
ample of  the  effect  of  vegetable  oils  when  used  on  roads,  may  be 
mentioned  an  experiment  with  oil  of  aloes  tried  in  Algiers  a  few 
years  ago.  The  oil  was  sprinkled  upon  the  surface  of  the  road 
in  its  natural  condition  for  the  purpose  of  laying  dust.  It  was 
found  that  the  dust  was  well  laid  for  a  considerable  length  of 
time  by  this  means,  but  that  in  wet  weather  an  oily,  slippery  mud 
was  produced  which  was  so  disagreeable  that  use  of  the  oil  for 
this  purpose  was  abandoned. 

Cotton  seed  oil  has  been  employed  to  some  extent  in  road 
preparations,  mainly  saponified  with  an  alkali  to  produce  a  soap 
solution  capable  of  acting  as  an  emulsifying  agent  for  mineral 
oils  and  tars.  Linseed  oil  and  rosin  oil  have  also  been  suggested, 
the  latter  forming  compounds  which  have  more  or  less  binding 
value.  One  patent  calls  for  the  addition  of  glue  and  bichromate 
of  potash  to  an  oil  preparation,  which  is  supposed  to  cause  it  to 
harden  upon  the  road  surface  under  the  action  of  light.  Such 
a  preparation  is  sold  in  England  under  the  name  of  Crempoid  D. 
These  substances  are  mentioned  not  because  of  their  value  as 
binders,  but  merely  to  show  the  variety  of  materials  which  have 
been  suggested  or  tried.  The  principal  value  of  vegetable  oils  and 
also  of  animal  oils  would  seem  to  lie  in  their  use  in  connection 
with  saponifying  materials  for  the  purpose  of  making  emulsions 
of  the  true  binding  bituminous  oils.  Such  emulsions  will  be  taken 
up  in  a  later  chapter. 

Animal  Oils  and  Fats.  —  The  same  objections  that  have  been 
made  to  the 'use  of  vegetable  oils  are  applicable  to  animal  oils 
and  fats.  Such  materials  carry  no  true  binding  base,  and  while 
they  are  excellent  dust  layers  the  mud  which  they  produce  in 
wet  weather  is  so  objectionable  as  to  have  discredited  their  use 
except  in  the  production  of  soaps  for  the  purpose  described  above. 

A  Scotch  preparation,  known  as  "Sandisize,"  which  has  been 
patented  both  in  England  and  this  country,*  deserves  mention 

*  U.  S.  Patent  No.  813,389.  Feb.  20,  1906. 


ORGANIC   NON-BITUMINOUS    DUST   PREVENTIVES         10$ 

as  having  been  employed  with  fairly  good  results  as  a  dust  layer. 
This  material  is  prepared  from  a  by-product  obtained  from  wool 
scourings  after  most  of  the  wax  has  been  extracted. 

Before  raw  wool  can  be  subjected  to  any  manufacturing 
process  it  must  be  washed  and  scoured  to  remove  impurities, 
which  are  present  to  the  extent  of  from  30  to  80  per  cent  of  the 
total  weight.  These  impurities  consist  of  yolk  or  wool  grease; 
suint,  composed  mainly  of  potassium  salts  of  oleic,  stearic, 
valeric  and  acetic  acids,  together  with  sulphates,  chlorides, 
phosphates  and  nitrogenous  bodies;  and  dirt  which  is  mechani- 
cally entangled  among  the  fibers.  These  substances  can  be 
removed  by  washing  the  wool  in  a  solution  of  soap.  Wool  is 
often  treated  to  recover  the  yolk  and  suint  separately,  accom- 
plished by  first  extracting  it  with  a  volatile  solvent  to  remove 
the  former  and  then  washing  it  to  dissolve  and  remove  the 
suint  and  dirt.  It  is  the  latter  product  which  is  mainly  em- 
ployed in  the  manufacture  of  Sandisize,  and  to  it  is  added 
caustic  potash  or  potassium  carbonate  and  an  oil  of  disin- 
fectant properties,  such  as  creosote  oil.  This  material  is  con- 
centrated and  sold  as  a  dust  preventive.  It  is  applied  to  the 
road  surface  in  diluted  form  by  means  of  a  sprinkler.  In  Scot- 
land the  cost  of  treating  one  mile  of  sixteen-foot  roadway  with 
a  10  per  cent  solution,  is  about  $21.50.  It  is  stated  that  three 
or  four  applications  per  season  will  effectively  lay  the  dust 
for  that  length  of  time.  Four  such  treatments  would,  there- 
fore, average  less  than  one  cent  per  square  yard,  which  is 
exceedingly  cheap.  The  number  of  treatments  necessary  will, 
however,  vary  with  local  conditions  so  that  in  some  cases  the 
cost  would  be  higher.  To  the  author's  knowledge  this  material 
has  not  as  yet  been  employed  in  this  country.  In  Scotland, 
where  it  has  been  most  extensively  used,  it  is  sold  in  concen- 
trated form  for  about  $30.00  per  ton. 

Waste  Sulphite  Liquor.  —  In  the  manufacture  of  wood  pulp, 
according  to  the  sulphite  process,  a  waste  liquor  is  produced  in 
large  quantities,  which  in  its  original  condition  is  not  only  of 
no  value,  but  a  nuisance  to  localities  near  which  it  is  pro- 


106  DUST   PREVENTIVES   AND    ROAD   BINDERS 

duced.  In  the  sulphite  process  wood  is  boiled  under  pressure 
in  a  digester  with  sulphurous  acid  or  more  commonly  with  an 
acid  sulphite,  of  calcium  and  magnesium.  By  the  action  of 
these  chemicals  the  lignin  and  other  incrusting  matters  of  the 
wood  fiber  are  broken  down  into  complex  substances  largely 
soluble  in  water.  Their  exact  composition  is  not  known,  but 
for  want  of  a  better  name  they  have  been  called  calcium  or 
magnesium  ligno-sulphonates.  The  solution  thus  produced  is 
known  as  waste  sulphite  liquor  and  is  usually  allowed  to  run 
to  waste  in  some  near-by  stream  where  it  pollutes  the  water, 
kills  fish  and  is  a  source  of  danger  and  annoyance. 

Crude  waste  sulphite  liquor  is  a  thin,  light  brown  liquid,  of 
slightly  acid  reaction  and  having  a  specific  gravity  of  from 
1.03  to  1.05.  If  it  is  evaporated  nearly  to  dryness,  a  gummy 
residue  is  obtained,  and  this  fact  has  suggested  its  use  as  a 
binding  medium.  While  the  crude  liquor  has  little  or  no  bind- 
ing value,  concentrated  liquors  exhibit  this  property  to  a  marked 
extent  and  recently  an  attempt  has  been  made  to  employ  them 
as  dust  layers  and  road  binders.  In  fact,  a  road  preparation 
containing  this  binding  medium  is  now  on  the  market  under 
the  name  of  Glutrin.  This  material  has  a  specific  gravity  of 
about  1.26  or  1.27  which  represents  a  concentration  of  the 
crude  material  to  about  one-fifth  of  its  original  volume.  Be- 
fore application  it  is  diluted  with  an  equal  quantity  of  water 
which  produces  a  solution  having  a  specific  gravity  of  1.13. 

The  cementing  value  developed  by  such  solutions  when 
mixed  with  rock  powders  is  shown  in  the  following  table.  In 
this  table  is  given  the  cementing  value  of  various  rock  powders 
with  water  alone  as  compared  with  their  cementing  value  when 
treated  in  the  same  manner  and  with  the  same  amount  of 
Glutrin  and  other  concentrated  sulphite  liquors  having  a  spe- 
cific gravity  of  1.13.  For  a  description  of  the  cementing  value 
test,  see  page  64.  The  crushing  strength  of  the  briquettes,  as 
made  for  the  cementing  value  test  and  determined  by  means 
of  a  small  Olsen  testing  machine  in  the  usual  manner,  is  also 
included  in  this  table  for  the  purpose  of  comparison. 


ORGANIC   NON-BITUMINOUS   DUST  PREVENTIVES        IO/ 


Roc 

k    Sample. 

Mixed  with 

Cementing 

Crushing 

No. 

Kind. 

Value. 

(Ibs.) 

2QOO 

Trap. 

Water  alone  

j  i 

368 

2OOO 

Trap. 

Glutrin  

IOOO-J- 

2477 

2QOO 

Trap. 

Concentrated  sulphite  liquor  A  

IOOO  + 

2IOO 

2900 

Trap. 

Concentrated  sulphite  liquor  B  

IOOO  + 

24.CO 

2901 

Gneiss. 

Water  alone  

27 

4l<r 

29OI 

Gneiss. 

Glutrin 

iooo-|- 

284.0 

2901 

Gneiss. 

Concentrated  sulphite  liquor  A 

800 

2  2  60 

2901 

Gneiss. 

Concentrated  sulphite  liquor  B  

iooo-|- 

220O 

2971 

Sandstone. 

Water  alone  

IO 

34.O 

2971 

Sandstone. 

Glutrin  

800+ 

OH-^ 

22f?8 
«so 

2971 
2971 

Sandstone. 
Sandstone. 

Concentrated  sulphite  liquor  A  
Concentrated  sulphite  liquor  B  

400 
690 

2260 
22SO 

From  these  results  it  will  be  seen  that  concentrated  sulphite 
liquors  act  as  powerful  road  binders.  As  the  binding  base  is, 
however,  soluble  in  water,  it  is  evident  that  frequent  rains 
will  tend  to  destroy  the  bond  and  remove  the  material  from  the 
road  surface.  This  is  demonstrated  by  the  fact  that  rock  dust 
briquettes  in  which  they  are  employed  slake  quite  readily  when 
immersed  in  water. 

In  order  to  overcome  this  difficulty,  attempts  have  been  made 
to  incorporate  with  the  sulphite  liquor  some  material  which 
after  it  has  dried  out  upon  the  road  will  waterproof  or  make 
insoluble  the  residual  base,  without  destroying  its  binding  value. 
The  best  results  along  this  line  have  been  obtained  by  the  use 
of  from  5  to  15  per  cent  of  a  semiasphaltic  road  oil,  showing 
the  following  characteristics: 

SEMIASPHALTIC   OIL. 

Specific  gravity  2$°/2$°  C 948 

Flash  point  °  C 197 

Loss  at  163°  C,  5  hours '. 2.80% 

Material  soluble  in  carbon  bisulphide,  total  bitumen 99.4  % 

Bitumen  insoluble  in  86°  paraffin  naphtha i .  50% 

Fixed  carbon i .  45% 


108  DUST   PREVENTIVES   AND    ROAD   BINDERS 

It  was  found  that  such  an  oil  could  be  readily  mixed  or  emulsi- 
fied with  the  sulphite  liquor  and,  when  employed  in  the  quanti- 
ties stated,  that  the  binding  base  was  made  almost  insoluble  after 
it  had  once  dried  out.  While  rock  dust  briquettes  made  with 
these  mixtures  showed  no  depreciation  in  cementing  value  when 
tested  dry,  and  while  they  did  not  slake,  it  was  noticed  that 
they  became  somewhat  soft  after  immersion  in  water  over 
night.  Oil  sulphite  liquor  mixtures  would  therefore  seem  to 
be  unsatisfactory  as  road  binders  in  wet  weather,  if  applied  to 
a  road  having  much  fine  material  upon  its  surface.  It  may  be 
added  that  the  use  of  such  mixtures  has  been  patented  *  as 
also  mixtures  of  waste  sulphite  liquor  with  deliquescent  salts 
such  as  calcium  chloride. 

As  has  been  stated,  crude  waste  sulphite  liquors  have  but  little 
binding  value,  and  when  applied  to  road  surfaces  are  hardly 
more  efficient  as  dust  layers  and  road  binders  than  water  alone. 
Their  use  is,  however,  covered  by  patent.! 

From  experiments  which  have  come  under  the  author's  notice, 
it  would  seem  that  concentrated  waste  sulphite  liquors  are 
suitable  for  use  only  upon  macadam  or  similar  roads.  When 
subjected  to  favorable  conditions,  they  may  be  considered  as 
semipermanent  binders,  although  more  than  one  application  will 
ordinarily  have  to  be  made  in  order  to  lay  the  road  dust  for  one 
season.  If  of  the  specific  gravity  mentioned,  1.26,  they  should 
be  diluted  with  an  equal  volume  of  water  and  applied  to  the  road 
surface  by  means  of  a  sprinkling  cart  at  the  rate  of  0.6  gallon 
solution,  or  0.3  gallon  of  the  original  material  per  square  yard. 
Before  application  the  road  should  be  swept  clean  if  much  dust 
is  present,  or  otherwise  the  solution  will  not  be  absorbed  by  the 
road  proper,  but  by  the  dust,  forming  a  hard  cake,  which  is  likely 
to  scale  off  in  dry  weather.  If  the  road  surface  is  fairly  clean, 
however,  it  will  readily  absorb  the  material  which,  upon  drying 
out,  binds  the  roadstones  firmly  together  until  eventually  re- 
moved by  rains.  A  road  so  treated  is  usually  slightly  darkened 
in  color  and  presents  a  hard  compact  surface. 

*  U.  S.  Patent  No.  865,578,  Sept.  10,  1907. 
f  U.  S.  Patent  No.  781,079,  Jan.  31,  1905. 


ORGANIC   NON-BITUMINOUS  DUST  PREVENTIVES          1 09 

Additional  treatment  will  be  required  from  time  to  time, 
depending  upon  local  conditions,  and  when  made  should  consist 
of  an  application  of  not  over  o.i  or  0.2  gallon  of  the  original 
material  per  square  yard,  made  in  suitable  dilution.  It  will  be 
found  that  results  of  similar  duration  to  the  first  treatment  will 
be  obtained  by  such  applications. 

Glutrin,  which  has  already  been  mentioned,  is  the  only  waste 
sulphite  liquor  preparation  that  has  been  employed  to  any 
extent  in  this  country  as  a  dust  preventive  and  road  binder.  It 
can  at  present  be  purchased  at  from  twelve  to  fifteen  cents  per 
gallon  f.o.b.  at  point  of  storage,  depending  upon  the  quantity 
ordered  and  whether  shipped  in  barrels  or  tank  car.  Taking 
the  minimum  figure  it  can,  therefore,  be  seen  that  application 
made  in  the  manner  above  described  will  cost  for  material  alone, 
excluding  freight,  not  less  than  four  cents  per  square  yard  for  the 
first  treatment  and  not  less  than  1.3  cents  per  square  yard  for 
each  succeeding  application. 

Molasses  Residues.  —  In  the  manufacture  of  sugar  from  sugar 
cane  a  by-product  is  obtained  which  is  known  as  black  strap,  or 
waste  molasses.  This  molasses  is  a  very  thick  syrupy  liquid, 
from  which  all  of  the  commercially  removable  sugar  has  been 
extracted.  It  contains  resinous  and  inorganic  constituents 
which  make  it  unfit  for  culinary  purposes.  A  small  amount  is 
used  for  feeding  cattle,  and  some  in  the  manufacture  of  rum,  but 
it  is  employed  mostly  as  a  fuel.  In  the  neighborhood  of  sugar 
factories  it  has  in  some  instances  been  experimentally  employed 
as  a  binder  for  cinder  paths  and  roads.  When  treated  with 
quicklime,  molasses  forms  compounds  of  high  binding  value 
known  as  calcium  sucrates.  Those  sucrates  are,  however,  soluble 
in  water  and  should,  if  possible,  be  waterproofed  before  being 
employed  as  road  binders.  Working  along  this  line  the  *  United 
States  Office  of  Public  Roads  conducted  an  experiment  at  Newton, 
Massachusetts,  during  the  summer  of  1908,  with  a  molasses, 
lime,  oil  mixture  as  a  road  binder.  A  description  of  this  experi- 
ment is  given  below  as  being  the  only  authentic  report  of  the 

*  Circular  No.  90,  Office  of  Public  Roads,  U.  S.  Dept.  of  Agriculture. 


110  DUST   PREVENTIVES   AND   ROAD   BINDERS 

use  of  molasses  as  a  road  binder.  While  the  results  obtained 
have  up  to  the  date  of  publication  of  this  book  proved  quite 
satisfactory,  too  short  a  time  has  elapsed  to  warrant  any  definite 
assertion  being  made  as  to  the  value  of  such  a  mixture  as  a  per- 
manent binder.  In  any  event,  however,  it  would  seem  that  in 
certain  localities,  preferably  dry,  where  molasses  may  be  obtained 
at  low  cost,  it  might  be  satisfactorily  employed  in  dilution  as  a 
dust  layer.  Waste  molasses  from  beet  sugar  refineries  should 
also  prove  serviceable  for  this  purpose. 

In  the  molasses,  oil,  lime  experiment  referred  to,  the  binder 
was  prepared  in  a  large  mortar  box  by  first  slaking  320  pounds 
of  quicklime  with  108  gallons  of  water.  As  soon  as  the  lime 
was  completely  slaked,  92  gallons  of  molasses  were  added  and 
thoroughly  mixed  with  it,  after  which  50  gallons  of  a  semi- 
asphaltic  oil  showing  the  following  analysis  were  stirred  in. 

SEMIASPHALTIC    OIL. 

Specific  gravity  2$0/2$0  C o .  994 

Flash  point  degrees  C 245 

Volatilization  tests, 

Loss  at  100°  C.,  5  hours o .  25% 

Loss  at  163°  C.,  7  hours 0.85% 

Loss  at  204°  C.,  7  hours 5 . 30% 

Residue 94 .  70% 

Character  of  residue Soft  semiasphaltic,  pulled  to  thread 

Material  soluble  in  carbon  bisulphide,  total  bitumen 99-85 

Organic  matter  insoluble .15 

Inorganic  matter o .  oo 


100.00 
Bitumen  insoluble  in  86  degrees  naphtha 5-45% 

While  the  preparation  was  still  hot  it  was  mixed  on  a  board 
with  cold  stone  in  the  proportion  of  18  gallons  of  the  prepara- 
tion to  960  pounds  of  ij-inch  to  f-inch  stone  to  350  pounds  of 
f-inch  stone  running  to  dust,  just  as  it  came  from  the  crusher. 
The  concrete  thus  produced  was  hauled  to  the  road  and  laid  upon 
a  prepared  broken  stone  foundation  as  soon  after  mixing  as 
possible.  It  was  applied  to  a  finished  depth  of  two  inches  and 
after  rolling  produced  a  firm,  resilient  surface  upon  which  heavily 


ORGANIC   NON-BITUMINOUS    DUST   PREVENTIVES         III 

loaded  wagons  produced  no  wheel  marks  one-half  hour  after  it 
was  laid.  Under  the  action  of  the  roller  a  small  portion  of  the 
oil  came  to  the  surface,  so  that  a  light  application  of  stone  chips 
was  required  to  put  the  surface  in  good  condition.  The  labor 
item  was  exceedingly  high  in  this  experiment,  because  of  the 
inexperience  of  the  workmen  in  preparing  and  .handling  the 
material.  The  total  cost  per  square  yard  in  excess  of  ordinary 
macadam  work  of  the  same  nature  was  about  twenty-two 
cents. 

Rosin  and  Resinates.  —  Some  tendency  has  been  shown  in 
patent  preparations  to  make  use  of  rosin  as  a  binding  medium. 
When  dissolved  in  or  combined  with  various  oils,  it  produces 
very  sticky  compounds  some  of  which  may  be  applied  in  the  form 
of  emulsions.  It  may  be  remarked  that  compounds  of  rosin 
with  lime  or  iron  have  been  employed  to  some  extent  in  the 
manufacture  of  artificial  stone.  These  compounds  are  known 
as  resinates  of  the  inorganic  bases  which  they  contain,  and  at 
the  present  time  are  of  interest  only  in  regard  to  their  possible 
use  as  permanent  road  binders.  Where  rosin  has  been  employed 
as  a  road  binder,  it  has  invariably  been  combined  with  other 
materials  so  that  it  is  hardly  possible  to  consider  its  application 
and  use  as  an  individual  substance. 

Summary  and  Conclusions.  —  In  this  chapter  a  number  of 
organic  non-bituminous  materials  have  been  considered  with 
reference  to  their  use  as  dust  layers  and  road  binders.  Of  these, 
waste  sulphite  liquor  is  probably  the  most  important,  owing  to 
the  fact  that  from  the  ordinary  standpoint  it  is  an  undesirable 
product  found  in  various  localities  throughout  this  country,  and 
should  be  quite  generally  available  at  small  cost.  Other  ma- 
terials such  as  vegetable  and  animal  oils  will  never  be  employed 
to  any  great  extent  for  this  purpose  and  are  relatively  unimpor- 
tant. Their  chief  value  seems  to  lie  in  their  soap  making  property 
when  treated  with  caustic  alkalies,  the  soaps  so  obtained  being 
employed  as  emulsifying  agents  for  true  binding  bituminous 
materials. 


CHAPTER  VI. 
HYDROCARBONS. 

THE  most  important  types  of  dust  preventives  and  road  bind- 
ers are  undoubtedly  to  be  found  among  the  large  and  varied 
class  of  substances  known  as  bitumens,  and  before  taking  up  the 
various  members  separately  with  relation  to  their  dust  laying 
and  road  binding  properties,  it  seems  necessary  for  a  proper 
understanding  of  the  subject  to  briefly  consider  their  chemical 
composition  and  constitution.  In  a  single  chapter  this  can  be 
done  only  in  a  very  general  way,  as  the  compounds  found  in  coal 
tar  and  petroleum,  together  with  their  derivatives,  constitute  the 
greater  part  of  our  present  organic  chemistry. 

Bitumens  as  a  class  are  composed  mainly  of  compounds  of 
carbon  and  hydrogen,  known  as  hydrocarbons,  together  with 
smaller  amounts  of  their  oxygen,  nitrogen  and  sulphur  deriva- 
tives. The  character  of  the  hydrocarbons  themselves  determines, 
to  a  great  extent,  the  physical  properties  of  the  bituminous 
materials,  and  some  knowledge  of  the  various  classes  of  hydro- 
carbons is,  therefore,  essential.  Only  the  typical  and  most  im- 
portant members  of  each  class  can  here  be  described,  but  it  is 
believed  that  this  will  enable  the  reader  to  obtain  a  fair  idea  of 
the  subject  as  a  whole  and  to  appreciate  and  understand  the 
differences  in  properties  of  the  various  bituminous  road  materials 
which  will  be  more  fully  discussed  in  later  chapters. 

The  Carbon  Atom.  —  Carbon  is  known  as  a  quadrivalent 
element;  that  is,  its  atom  has  four  valences  or  unsatisfied  affinities 
ready  to  unite  with  other  atoms  or  radicals  to  form  compounds. 
It  is  commonly  represented  by  the  letter  C  surrounded  by  four 
dashes,  each  dash  denoting  a  valence: 

•I 
—  C  — 


112 


HYDROCARBONS  113 

The  carbon  atom  is  capable  of  combining  with  hydrogen  under 
favorable  conditions  to  form  a  hydrocarbon  molecule  or  com- 
pound. As  hydrogen  (H)  is  a  monovalent  element,  having  but  one 
combining  link  or  valence,  and  as  all  of  the  valences  in  a  molecule 
must  be  satisfied  by  union  with  the  valences  of  other  atoms,  it 
is  evident  that  four  hydrogen  atoms  are  required  to  satisfy  the 
carbon  atom  and  that  the  compound  thus  produced  must  have 
the  formula  CH4.  This  may  be  considered  as  the  parent  hydro- 
carbon, and  may  be  graphically  expressed  as  follows: 

H 

I 

H-C-H. 

I 
H 

Besides  its  ability  to  combine  with  hydrogen  the  carbon  atom 
can  unite  with  other  carbon  atoms  and  it  may  do  this  in  three 
ways,  either  by  a  single,  double  or  triple  linkage,  as  follows: 

(i)    ;C-C^     (2)-C-C=     (3)-C=C-. 

The  remaining  valences  may  then  be  taken  up  by  hydrogen 
atoms  to  form  the  corresponding  hydrocarbons,  C2H6,  C2H4, 
C2H2. 

H    H 

II  H  H 

(i)  H-C-C-H     (2)        /C  =  C^       (3)  H-C=C-H. 
II  IT  XH 

H     H 

Instead  of  hydrogen  atoms,  other  carbon  atoms  may  be  taken 
up  in  an  almost  limitless  number  and  according  to  any  of  the 
three  methods  of  linkage  made  possible  by  the  free  valences 
present.  Thus  we  may  have 

H   H    H  H    H     H    H 

II  I       I       I       I 

H-C-C-C-H  H-C-C-C-C-H,  etc. 

III.  I       I       I       I 

H    H    H  H     H     H    H 


114  DUST  PREVENTIVES   AND   ROAD   BINDERS 

When  the  linkage  of  carbon  atoms  is  open  at  both  ends,  as  in 
the  preceding  examples,  the  compounds  are  known  as  open 
chain  hydrocarbons.  The  carbon  atoms  may,  however,  be  joined 
together  so  as  to  form  a  closed  chain  or  ring,  in  which  case  they  are 
called  cyclic  hydrocarbons.  Examples  of  the  more  simple  ring 
compounds  are  as  follows: 

H     H 

/~«  -tl-2^-x 

H        /  \       H  '       ' 

X      _      /  i!Lx 


In  the  ring  compounds,  as  in  the  open  chain  compounds,  the 
carbon  atoms  may  be  united  by  a  double  as  well  as  a  single  bond. 
In  either  class  when  the  bonds  are  all  single  the  compound  is 
said  to  be  saturated.  When  a  double  or  triple  union  occurs, 
however,  the  compound  is  called  unsaturated,  because  the  extra 
valences  between  the  carbon  atoms  are  not  taken  up  by  other 
atoms.  The  unsaturated  compounds  are  as  a  rule  less  stable 
chemically  than  the  saturated,  and  many  of  them  are  capable 
of  reacting  with  various  substances  in  such  a  way  as  to  break 
down  the  double  or  triple  bond  and  form  saturated  compounds. 

In  the  study  of  organic  chemistry,  it  is  customary  to  separate 
the  hydrocarbons  into  two  main  classes:  (i)  open  chain  and  (2) 
cyclic;  and  to  subdivide  each  of  these  classes  into  two  groups; 
(a)  saturated,  and  (b)  unsaturated.  This  method  will  be  adhered 
to  in  the  following  brief  consideration  of  those  hydrocarbons 
which  are  of  typical  occurrence  in  bituminous  road  binders. 

I.     OPEN  CHAIN  HYDROCARBONS. 

(a).  Saturated.  —  The  saturated  open  chain  hydrocarbons  are 
commonly  known  as  paraffins.  They  constitute  a  series  of 
compounds  the  simplest  member  of  which  is  CH4,  which  has 
already  been  mentioned.  This  compound  is  known  as  methane 
or  marsh  gas.  The  next  member,  C2H6,  is  known  as  ethane,  the 
third,  C3H8,  as  propane,  the  fourth,  C4H10,  as  butane,  the  fifth, 


HYDROCARBONS 


C5H12,  as  pentane,  etc.  It  will  be  noticed  that  each  member  dif- 
fers from  the  preceding  member  by  CH2.  In  other  words,  they 
constitute  an  homologous  series  with  a  constant  difference  of 
CH2,  and  their  general  formula  may  be  expressed  as  CnH2n+2. 
By  a  glance  at  the  following  graphic  formulae  it  will  also  be  seen 
that  each  succeeding  member  may  be  considered  as  formed  from 
the  preceding  member  by  the  replacement  of  one  of  its  hydrogen 


atoms  by  CH3. 

Thus: 

H 

H 

"H 

1 

1 

1 

H-C-H 

H-C- 

C-H 

1 

1 

1 

H 

H 

H 

Methane. 

Ethane. 

H    H    H 

H    H 

I       I 
H-C-C- 

I       I 
H    H 


H 

I 

C-H 
I 
H 


Propane. 


I         I 


H 


C-H. 


H 


H-C-C-C- 

I       i       I 
H    H    H 

Butane. 

CH3  can,  therefore,  be  considered  as  a  radical,  or  group  of 
atoms  corresponding  to  an  atom  with  a  single  valence.  In 
like  manner  CH2  can  be  considered  as  a  bivalent  radical  and 
CH  as  trivalent.  These  radicals  derive  their  names  from  the 
parent  hydrocarbon,  methane,  and  similar  radicals  are  derived 
from  the  other  members  of  the  series.  Thus: 

Methenyl. 


Methane. 

Methyl. 

Methylene. 

CH4 

-CH3 

=  CH2 

Ethane. 

C2H0 

Ethyl. 

-C2H5 

Ethylene. 

Propane. 

C3H8 

Propyl. 

-C.H, 

Propylene. 

Ethenyl. 


Propenyl. 


If  the  number  of  carbon  atoms  in  the  open  chain  compounds 
is  greater  than  three,  their  relative  position  to  one  another 
may  vary  so  as  to  produce  different  compounds  having  the 
same  number  of  carbon  and  hydrogen  atoms,  but  differing 
somewhat  in  their  chemical  and  physical  properties.  Such  com- 


Il6  DUST   PREVENTIVES   AND    ROAD    BINDERS 

pounds  are  known  as  isomers.     Thus  C4H10  may  exist  in  two 
modifications  as  shown  by  the  formulas, 

H    H    H    H  H    H    H 

till  III 

H-C-C-C-C-H     and      H-C-C-C-H. 

till  II 

H    H    H    H  H  H 

H-C-H 
I 
H 

Normal  Butane.  Iso  Butane. 

In  the  latter  case  a  side  chain  is  introduced  and  the  relative 
position  of  the  carbon  atoms  changed. 

It  is  evident  that  as  the  number  of  carbon  atoms  increases, 
the  number  of  possible  isomers  increases  rapidly.  Thus  three 
isomers  are  possible  for  pentane  (C5H12) : 

CH3 
I 
CH3-CH2-CH2-CH2-CH3         CH3-CH-CH2-CH3 

Normal  pentane.  Iso  pentane. 

CH3 
I 
CH3-C-CH3, 

I 
CH3 

Tetra  Methyl  Methane. 

The  next  member,  hexane  (C6H14),  has  6  isomers,  while  tridec- 
ane  (C13H28)  has  802  isomers.  It  is  thus  seen  that  the  number 
of  different  paraffin  hydrocarbons  is  enormous.  The  known 
normal  paraffins  alone  run  as  high  as  C00H122,  and  the  possible 
isomers  for  this  compound  are  almost  beyond  comprehension, 
except  in  a  comparative  way.  Some  idea  can,  therefore,  be 
obtained  at  this  point  of  the  futility  of  attempting  to  determine 
the  presence  of  isolated  compounds  in  bituminous  road  mate- 
rials which  are  themselves  extremely  complex  mixtures  of  the 
paraffin  and  various  other  hydrocarbon  series  in  varying  pro- 
portions. The  presence  and  especially  the  predominance  of 


HYDROCARBONS 


II/ 


certain  series  can,  however,  be  ascertained  either  directly  or 
indirectly,  and  this  is  often  a  valuable  aid  in  determining  the 
road  building  properties  of  the  material. 

The  lowest  members  of  the  paraffin  series  up  to  C4H10  are 
gases  at  ordinary  temperature,  and,  therefore,  need  not  be 
considered  in  relation  to  road  preparations.  The  intermedi- 
ate members,  from  C5H12  to  C15H32,  are  colorless  oily  liquids,  and 
the  higher  members,  beginning  with  C16H34,  are  greasy  crys- 
talline solids. 

The  melting  and  boiling  points  of  the  known  normal  paraf- 
fins from  pentane  up,  as  given  by  Richter,*  are  shown  in  the 
following  table.  It  should  be  noted  that  the  higher  members 
from  C20H42  up  are  only  volatile,  without  decomposition,  under 
reduced  pressure. 


Name 

Formula. 

Melting 
Point, 
Degrees  C. 

Boiling  Point, 
Degrees  C. 

Pentane 

C,H12 

38 

98.4 
125.5 
149-5 
173        I 
194.5 
214 

234 

252.5 
270.5 
287.5 
3°3 
3i7 
33°       J 
205       ' 

215 
224.5 

234 
243 

270 
302 
310 
33i 

Under  15  M.M.  pressure  Under  760  M,M.  pressure 

Hexane          ...        .    . 

C0HU 
C7Hlfi 

Heptane  

Octane  

C,H18 

Nonane 

cfL 

CioHza 
CnH24 

^12^G 

CA 

C^Hgo 

£15^32 

Cl6H34 

C17H3C 

c18!"38 

<--l  9^40 

C2oH42 

C21H44 
Q>2H46 

Q3H48 

CA 
W^SG 

C31H64 

MS11  66 

Car,H72 

^60**122 

-51 
-32 
-26.5 

—  12 

-   6.2 

+  5-5 

10 

18 
22.5 
28 
32 

36.7 
40.4 
44.4 
47-7 
Si.i 
59-5 
68.1 
70.0 

74-7 
1  02 

Decane 

Undecane 

Dodecane    

Tridecane  

Tetradecane  

Pentadecane  

Hexadecane 

Heptadecane.    . 

Octadecane  

Nonadecane  

Eicosane  

He  neicosane 

Docosane.  .  .  . 

Tricosane          

Tetracosane  

Heptacosane  

Hentriacontane 

Dotriacontane 

Pentatriacontane 

Dimvricyl  

*  "Richter's  Organic  Chemistry"  (Smith),  3d  Ed.,  Vol.  i,  p.  86.     Blackiston's 
Sons  &  Co. 


Il8  DUST  PREVENTIVES   AND   ROAD    BINDERS 

All  of  the  paraffin  hydrocarbons  are  insoluble  in  water.  The 
lower  and  intermediate  members  are  readily  soluble  in  alcohol 
and  ether,  but  the  higher  members  are  less  soluble,  especially 
at  low  temperatures,  and  this  fact  has  been  made  the  basis  of  a 
determination  for  paraffin  scale  which  will  be  described  in  a 
later  chapter. 

Liquid  paraffins  may  be  separated  from  hydrocarbons  of 
most  of  the  other  series  by  treatment  with  sulphuric  acid 
as  long  as  the  acid  becomes  colored  and  then  with  fuming 
nitric  acid.  Other  substances  are  oxidized  or  converted  into 
compounds  which  are  dissolved  by  the  acids  while  the  par- 
affins remain  unaltered  and  may  be  separated  by  suitable 
means. 

The  paraffin  hydrocarbons  occur  principally  in  petroleum, 
although  they  are  also  found  to  some  extent  in  the  products  of 
destructive  distillation.  They  are  for  the  most  part  undesir- 
able constituents  when  present  in  large  quantities  in  road 
binders,  as  will  appear  later. 

(b).  Unsaturated.  —  The  unsaturated  open  chain  compounds 
may  be  divided  into  two  main  classes,  (i)  those  containing 
two  carbon  atoms  doubly  linked,  and  (2)  those  containing  two 
carbon  atoms  trebly  linked.  The  former  are  known  as  olefines 
and  the  latter  as  acetylenes.  Both  constitute  an  homologous 
series  with  a  constant  difference  of  CH2  between  adjoining 
members  as  in  the  paraffin  series.  Other  series  containing 
two  double  linkages,  known  as  diolefines,  and  two  treble 
linkages,  known  as  diacetylenes,  likewise  exist,  but  need  not  be 
considered  separately.  Compounds  with  both  double  and 
treble  linkages  are  also  known  and  these  are  called  olefina- 
cetylenes. 

Olefines.  —  The  first  member  of  the  olefine  series,  C2H4,  is  ethy- 
lene,  the  second,  C£H0,  propylene,  the  third,  C4H8,  butylene. 
They  may  be  graphically  expressed  as  follows  and  it  will  be 
seen,  as  in  the  case  of  the  paraffins,  that  each  member  may  be 
considered  as  formed  from  the  preceding  one  by  the  replace- 
ment of  one  of  its  hydrogen  atoms  by  the  radical  CH3. 


HYDROCARBONS 


CH2  =  CH2        CH2  =  CH  .  CH2        CH2 


CH  .  CH2 .  CH3. 

Ethylene  Propylene  Butylene 

The  general  formula  for  this  series  of  hydrocarbons  is  CnH2n. 

Beginning  with  butylene,  isomers  are  encountered  and  for 
the  formula  C4H8  we  may  have 

/CH3 
CH2=  CH.CH2.CH3  CH3.CH  =  CH  .  CH  3  CH2=c' 

CH3 

Normal  butylene  or  Symmetrical  dimethyl  Unsymmetrical  di- 

ethyl  ethylene  ethylene  methyl  ethylene 

For  the  higher  members  a  rapidly  increasing  number  of 
isomers  exists.  The  first  three  members  of  the  ethylene  series 
are  gases  at  ordinary  temperatures,  the  intermediate  members 
liquids  and  the  higher  members  solids.  The  boiling  points  of 
the  known  olefines  which  have  been  shown  by  Shorlemmer  to 
exist  in  American  petroleums  are  given  in  the  following  table. 
Some  of  these  are  also  found  in  coal  tars  and  oil  tars. 


Name. 

Formula. 

Boiling 
Point, 
Degrees  C. 

Gaseous. 
Ethylene  

CoH 

Propylene  

C,H« 

—  18 

Butylene  

C,He 

4-  3 

Fluid. 
Amylene  

CeH 

Hexylene  

C.H  „ 

OJ 

60 

Heptylene  

C,H,« 

Qf 

Octylene  

C0H,« 

yj 

IO<1 

Nonylene.  .  . 

CH 

Decatylene  

CH 

160 

Endecatylene  

C   H 

Dodecatylene  «. 

C  .H  „ 

*yj 

Decatritylene  

21Z 

Cetene  

^oo 

271 

C  H 

*  IJ 

Solid. 
Cerotene  

^20Ai40 

Co,H  , 

Melene  

•37^ 

In   chemical  properties  the  olefines  differ  greatly  from  the 
paraffins.     Concentrated  sulphuric  acid  absorbs  them,  forming 


120 


DUST  PREVENTIVES   AND   ROAD   BINDERS 


ethereal  salts  and  other  addition  products,  and  this  reaction  can 
be  used  to  separate  them  from  the  paraffins.  In  themselves 
they  are  probably  of  little  value  when  present  in  road  binders, 
but  if  found  in  appreciable  quantities  are  indicative  of  at  least 
an  approach  towards  suitable  road  binders.  They  are  of  pecul- 
iar interest  in  respect  to  their  relation  to  the  saturated  ring 
hydrocarbons  of  like  carbon  contents,  known  as  naphthenes, 
which  have  the  same  general  formula  and  may  therefore  be 
considered  as  their  isomerides. 

Acetylenes.  —  The  acetylene  series  takes  its  name  from  the 
first  of  its  members,  C2H2.  Each  member  following  differs  from 
the  preceding  by  CH2  and  the  general  formula  for  this  series 
is,  therefore,  CnH2«_2.  Thus: 

CH  =  CH        CH  =  C-  CH3     CH3-  C  =  C  —  CH3. 

Acetylene.  Allylene.  Crotonylene. 

Isomeric  modifications  begin  with  crotonylene,  the  third  mem- 
ber. The  following  table  gives  the  boiling  points  of  some  of 
the  acetylenes. 


Name. 

Formula. 

Boiling 
Point, 
Degrees  C. 

Acetylene  

CH  =  CH 

Gas 

Allylene 

CH  C  =  CH 

Gas 

Crotonylene 

CH3C  =  C    CH 

27—28 

Ethyl  acetylene  

CoELC  =  CH 

18 

Methyl  ethyl  acetylene  

C2H5C  =  C    CH3 

r  r—  r6 

Normal  propyl  acetylene  

CSH7C  =  CH 

4.8—4Q 

Isopropyl  acetylene   . 

(CH  )2CH    C  =  CH 

28-20 

While  acetylenes  are  found  to  a  limited  extent  in  some  classes 
of  petroleum,  their  presence  in  tars  is  of  more  interest  in  rela- 
tion to  their  close  connection  with  the  formation  of  the  benzene 
series  of  hydrocarbons  which  .are  unsaturated  ring  compounds 
having  an  entirely  different  general  formula. 

Thus  at  high  temperatures  three  molecules  of  C2H2  may 
polymerize  to  form  a  single  molecule  of  C6H6,  benzene,  which 


HYDROCARBONS  121 

will  be  described  later  under  another  series  of  hydrocarbons. 
Polymerism  may  be  considered  as  isomerism  of  bodies  of  dif- 
ferent molecular  mass,  or  the  aggregation  of  two  or  more  like 
molecules  into  a  new  molecule.  Members  of  many  of  the  series 
of  hydrocarbons  are  known  to  polymerize  under  favorable  con- 
ditions. Paraffin  hydrocarbons,  however,  cannot  polymerize,  as 
has  been  proved  by  Mayberry,  for  a  multiple  of  any  compound 
having  the  formula  CrtH2n+2  would  no  longer  preserve  the  ratio 
of  carbon  to  hydrogen  observed  among  the  paraffins. 

II.     CYCLIC   HYDROCARBONS. 

(a).  Saturated. — The  saturated  cyclic  hydrocarbons  are  known 
as  polymethylenes.  The  bonds  between  the  adjacent  carbon 
atoms  are  of  course  single.  The  polymethylenes  may  most 
conveniently  be  considered  under  two  divisions  according  to 
their  structure,  (i)  those  which  consist  of  one  cycle  only,  and 
(2)  those  consisting  of  more  than  one  cycle.  The  former  are 
called  naphthenes,  or  monocyclic  polymethylenes,  and  the  latter 
polycyclic  polymethylenes.  The  monocyclic  polymethylenes 
constitute  an  homologous  series,  the  dicyclic  another,  the  tricy- 
clic  a  third,  etc.  They  are  found  particularly  in  oils  of  asphaltic 
characteristics  and  in  the  solid  native  bitumens. 

Naphthenes.  —  While  the  simple  monocyclic  polymethylenes 
may  be  composed  of  any  number  of  methylene  (CH2)  radicals, 
from  three  to  seven  united  in  a  single  ring,  it  is  to  the  hexa- 
methylenes,  or  hexahydrobenzenes  as  they  are  often  called,  that 
the  term  naphthenes  is  mainly  applied.  The  first  member  of 
the  naphthene  series  is  hexamethylene  (C6H12),  and  the  other 
members  may  be  considered  as  being  formed  from  it  by  the 
replacement  of  one  or  more  of  its  hydrogen  atoms  by  CH3  or 
other  open  chain  radicals.  It  is  isomeric  with  methyl  penta- 
methylene,  as  shown  below. 

CH2  •  CH2  CH2  •  CH2 

CH2(  )CH2  I  )CH.CH3. 

CH2-CH2  CH2  -CH2 

Hexamethylene  Methyl  Pentamethylene 


122 


DUST  PREVENTIVES   AND   ROAD   BINDERS 


The  next  two  members  may  be  represented  as  follows,  and 
are  seen  to  consist  of  a  single  ring  radical  in  combination  with  an 
open  chain  radical. 


CH 


CH2.  CH2 


2\ 


CH2-  CH2 


)CH-CH3 


CH 


CH2-CH2x 
2XCH2-CH/ 


CH.CH2CH3. 


Methyl  Hexamethylene  or  Ethyl  Hexamethylene  or 

Hexahydrotoluene  Hexahydroxylene 

The  constant  difference  CH2  exists  between  the  adjacent  mem- 
bers, and  the  general  formula  is,  therefore,  CnH2n  which  is  the 
same  as  that  of  the  olefines. 

Isomers  of  many  of  these  members  have  been  isolated  and  the 
number  of  possible  isomers  is  almost  limitless.  The  boiling 
points  of  the  first  nine  members  and  some  of  their  isomers,  as 
given  by  Markownikoff ,*  are  shown  in  the  following  table.  These 
hydrocarbons  have  been  isolated  from  certain  types  of  petro- 
leums. 


Name. 

Formula. 

Boiling 
Point, 
Degrees  C. 

Hexahydrobe  nze  ne  . 

C.H,o 

60 

Hexahydrotoluene  

CH     

wy 
QC—  Qo 

Hexahydro-m-xylene  .    . 

CoH,«. 

I  I  ^—124 

Hexahydromesitylene  1 
Hexahydro-^-cumene  

C0H 

I35-I38 
I7C—  178 

Hexahydropropylbenzene  . 

I4O—  142 

Dodecahydronaphthalene  . 

C    H 

I  ^3~I  7O 

cXT 

I  7Q—  l8l 

107 

(~*   TT 

240—241 

246—248 

Although  not  as  stable  as  the  paraffin  hydrocarbons,  the 
naphthenes  are  not  acted  upon  by  sulphuric  acid.  The  higher 
members  are,  however,  more  reactive  than  the  lower.  They 
do  not  solidify  at  low  temperatures  and  are  separated  from  the 
paraffins  by  freezing  and  filtration.  The  naphthenes  are  found 
principally  in  Russian  petroleum,  although  they  exist  to  some 
extent  in  American  petroleums  as  well  as  tars. 

*  Jura.  Russk.  Ph.-Kh.  Obsch.,  XV,  237  (1883),  and  XXIV,  141  (1892). 


HYDROCARBONS  1  2  3 

Poly  cyclic  Polymethylenes.  —  In  the  poly  cyclic  polymethy- 
lenes  two  or  more  rings  are  found  which  have  a  number  of 
carbon  atoms  common  to  both.  Examples  of  this  are  shown 
by  the  following  known  compounds,  which  are  said  to  have  a 
bridge  structure. 

CH2-  C(CH3)  -  CH2  CH2-  CH  -  CH2 

II  I  II  I  CH. 

CH2     CH2  CH2  CH2     CH-CH3CHCH( 

II  I  II  I  CH, 

CH2  -  CH  -       -  CH2  CH2-  CH  -      -  CH2 

C10H18,  Methyl-bicyclo-nonane  C13H24,  Isopropyl-methyl-bicyclo-nonane- 

Both  of  these  hydrocarbons  belong  to  the  CnH2n_2  series  of 
saturated  compounds.  But  little  is  known  of  the  various 
members  of  this  and  many  other  series  of  polycyclic  polymethy- 
lenes  and  their  constitution  is  largely  a  matter  of  theory.  They 
may  in  general  be  said  to  occur  in  petroleums  of  an  asphaltic 
nature  and  in  the  native  asphalts.  The  higher  members  are 
extremely  complex. 

(b).  Unsaturated.  —  There  are  quite  a  large  number  of  un- 
saturated  cyclic  hydrocarbon  series,  but  only  three,  which  are 
of  the  most  importance  in  the  study  of  road  binders,  will  be 
taken  up  in  any  detail.  The  nucleus  of  these  hydrocarbons,  which 
are  known  as  the  benzene,  the  naphthalene  and  the  anthracene 
series,  is  the  benzene  ring,  which  consists  of  six  carbon  atoms  joined 
together  with  alternate  single  and  double  linkages  as  shown: 

I 

C 
-C'     XC- 

I         II  . 

-C  C- 


Each  carbon  atom  has  one  free  valence  which  may  be  taken 
up  by  hydrogen  or  various  univalent  radicals.  In  spite  of  the 
fact  that  three  double  linkages  are  present,  this  ring  is  compari- 
tively  stable  and  remains  intact  during  most  reactions.  Under 
suitable  conditions  it  can,  however,  be  broken  down  to  the 


124  DUST  PREVENTIVES  AND  ROAD  BINDERS 

saturated  hexahydrobenzene  nucleus  which  has  been  encountered 
under  the  naphthenes. 

Benzene  Series.  —  The  first  member  of  the  benzene  series  is 
benzene  (C6H6)  or  benzol  as  it  is  often  called.  The  next  member 
is  toluene  (C7H8),  and  the  third  xylene  (C8H10).  They  may  be 
graphically  expressed  as  follows: 

H  CH3  CH3 

I  I  I 

H.C  HH  C          HH  C 

\   ^-t  ^r  ^\    s~\    /  N   f\  ^r  ^\    s~\   f  ^\    s~\  ^  >    *~\  /"^TT 

\^  ^  L/  U  U  \~> — ^-t!3 

I  II  I  II  I  II 

/C\      /C\  /C^      /C\  /C\      /C\ 

I  I  I 

H  H  H 

Benzene.  Toluene.  Xylene. 

The  constant  difference  CH2  is  found  between  the  members  of 
this  series  whose  general  formula  is  CnH2n_6.  Beginning  with 
xylene,  isomers  are  encountered,  there  being  four  for  this  com- 
pound. Thus  the  formula  given  above  is  that  representing 
orthoxylene,  which  is  a  dimethyl  benzene.  The  other  three  are 
as  follows: 

CH3  CH3 

I  I 

C  C 

H-C^     XC-H  H-C^    XC  — H 

I  II  I  II 

H-C^     xC-CH3  H~C^     /C~H 

I  I 

H  CH3 

Meta  Xylene.  Para  Xylene. 

CH2  •  CH3 
I 

C 
H-CT     XC-H 

I        II 

H-C^     /C-H 

I 
H 

Ethyl  Benzene. 


HYDROCARBONS 


125 


Benzene  (C6H6)  is  the  parent  hydrocarbon  of  the  so-called 
aromatic  compounds.  It  is  a  mobile  ethereal  liquid  with  a 
characteristic  odor,  having  a  definite  boiling  point.  It  should 
not  be  confused  with  benzine,  which  is  the  term  applied  to 
the  lighter  and  more  volatile  fractions  of  petroleum,  consisting 
mainly  of  the  paraffin  series.  The  melting  and  boiling  points 
of  some  of  the  most  important  members  of  the  benzene  series 
are  given  in  the  following  condensed  table  taken  from  Richter's 
Organic  Chemistry. 


Name. 

Formula. 

Melting 
Point, 
Degrees  C. 

Boiling 
Point, 
Degrees  C. 

Benzene 

C*H 

80  A 

Toluene.  ... 

C  TT  CH 

•4 

m-Xylene  (Isoxylene) 

CJLCCHJo 

—  r/i 

Ethyl  benzene  

C6H5  •  CH2CH, 

o* 

ioy 

I  ?A 

Trimethyl  benzenes.  

C«H,(CH.), 

M4 

(i,  2,  4)  =  pseudocumene  

I7O 

(r>  3>  5)  =  mesitylene  

164.    ^ 

Isopropyl  benzene  (Cumene)  
Cymene    .  . 

C6H5CH(CH3)2 
C-H,  •  CCH  KC  H,") 



153 

Pentamethyl  benzene 

CCH  •  CCH  ). 

C  2 

^/j 
2  2O 

Hexamethyl  benzene  .... 

C«(CH,)« 

l6d 

'J" 

264. 

Pentaethyl  benzene  

CAH(C,H,)« 

277 

Hexaethyl  benzene  

C.CCoH,). 

I2O 

2O8 

Members  of  the  benzene  series  of  hydrocarbons  have  been 
isolated  from  certain  petroleums,  but  it  is  in  the  products  of 
destructive  distillation  that  their  occurrence  is  of  most  interest. 
They  react  with  sulphuric  acid  to  form  sulphones,  or  sulphonic 
acids  and  water.  Just  as  CH3  or  any  univalent  chain  radical 
may  replace  a  hydrogen  atom  of  the  benzene  ring,  so  also  may 
a  univalent  closed  chain  radical,  and  when  this  occurs  com- 
pounds having  more  than  one  ring  nucleus  are  found.  Thus  we 
may  have  what  are  known  as  the  polyphenyl  hydrocarbons. 

Polyphenyls.  —  The  simplest  member  of  this  group  of  hydro- 
carbons is  diphenyl,  so  called  because  it  is  composed  of  two 
phenyl  radicals  joined  together.  Phenyl  (C6H5)  may  be  con- 
sidered as  benzene  from  which  one  hydrogen  atom  has  been 


126  DUST   PREVENTIVES   AND   ROAD   BINDERS 

removed.     The  formula  for  diphenyl  is,  therefore,   C12H10  or 
graphically  expressed  : 

H  H 

I  I 

C  C 


|  II  ii 

H-C          C  C        ,C-H 

%r/     \      /     \r^ 

I          HH          | 
H  H 

As  might  be  expected  from  a  consideration  of  the  other  series 
of  compounds,  the  next  member  of  the  diphenyl  series  is  methyl 
diphenyl  or  phenyltolyl,  having  the  formula  C13H12,  which  differs 
from  diphenyl  by  CH2.  The  general  formula  for  this  series  is, 
therefore,  CnH2n_14.  Its  various  members  are  found  most 
commonly  in  tars.  More  complicated  compounds  containing 
three,  four  or  more  benzene  nuclei-  are  known  but  these  need 
not  here  be  considered. 

Naphthalene  Series.  —  The  naphthalene  series  is  composed  of 
hydrocarbons  having  two  benzene  nuclei  condensed  to  a  single 
nucleus,  two  carbon  atoms  being  common  to  both.  Somewhat 
similar  examples  were  noted  in  the  polycyclic  polymethylene 
bridge  compounds  described  above,  where  three  carbon  atoms 
were  common  to  both  rings.  The  first  member  of  the  naph- 
thalene series  is  naphthalene  itself,  having  the  formula  C]0H8, 
and  graphically  expressed  as  follows: 

H          H 

I  I 

C  C 

H-C^     XCX     ^C-H 

Hi- 
H-C  C        ,C-H 

C7     ^C 

I        I 

H          H 

Naphthalene  is  found  principally  in  coal  tar.  It  is  a  crystal- 
line compound  highly  volatile  and  possessing  a  peculiar  odor. 
Its  presence  is  probably  detrimental  in  certain  classes  of  road 


HYDROCARBONS  I2/ 

binders  and  this  fact  will  be  discussed  in  a  later  chapter. 
Methyl-naphthalene  (CUH10)  is  the  next  member  of  this  series  and 
occurs  in  two  isomeric  modifications,  alpha  and  beta,  according 
to  the  position  of  the  methyl  radical  with  respect  to  the  carbon 
atoms  common  to  both  benzene  rings.  The  general  formula  for 
this  series  is  CnH2n_12. 

Anthracene  Series.  —  In  the  anthracene  series  three  benzene 
rings  are  condensed  to  a  single  nucleus  and  the  first  member, 
anthracene  (C14H10),  may  be  represented  as  follows: 


H          H           H 

1                          1 

c        c        c 

JJ  

c'   xcx 

^r/     V- 

v^                   v^ 

H 

1        II 

II         1 

.  . 

H- 

c,      c 

c        c- 

H 

I       I       I 

H          H  H 

Like  naphthalene  anthracene  is  also  a  crystalline  solid,  found 
principally  in  tars  which  have  been  produced  at  high  tempera- 
tures. Methyl  anthracene  (C6H4:  (CH)2  :  C6H3.  CH3)  is  the  next 
member  of  the  series,  whose  general  formula  is  CnH2n_18. 

Other  Series  of  U maturated  Hydrocarbons.  —  Besides  those 
already  mentioned,  other  series  holding  an  intermediate  position 
between  the  benzenes  and  naphthalenes,  and  naphthalenes  and 
anthracenes,  also  exist  and  have  been  found  in  bituminous  mate- 
rials. Thus  theolefine  benzenes,  of  which  styrolene  (C6H.CH :  CH2) 
is  the  parent  hydrocarbon,  have  the  general  formula  CnH2n_8. 
The  indene  group  (CnH2n_1&),  of  which  indene  (C9H8)  is  the  first 
member,  has  a  condensed  nucleus  as  shown  below: 

H 

I 
C 

HC*  ^        ^  C*  C*         XT 

~  \^  \^ U —  ±1 

.          I  II  II 

H-C  C        C-H 

^>P /     \  / 

[  CH2 

H 


128  DUST   PREVENTIVES   AND   ROAD  BINDERS 

The  acenaphthene  series  (CnH2n_14)  has  a  still  more  compli- 
cated nucleus,  as  shown  by  the  graphic  formula  for  its  first 
member  acenaphthene  (C12H10),  expressed  as  follows: 


•2^ 

V^ii2 

1 

1 

C 

c 

f 

XC 

/     ^p 

H 

II 

1 

•f 

„ 

/C 

\    e- 

H 

1 

i 

H 

H 

H-C 


The  fluorene  group  forms  still  another  series,  having  the 
general  formula  C?!H2n_16.  Its  first  member,  fluorene,  is  believed 
to  have  the  following  constitution: 

H  H 

I  I 

C  C 

H-C^    NC  —  C/     V-H 

I  II         II  I 

H-  C  C        C  C-  H 

^£/  \      /  ^C* 

I  CH2  | 

H  H 

Some  members  of  all  of  these  series  are  known  to  exist  in 
coal  tar  and  many  have  been  found  in  various  mineral  oils  and 
asphalts.  They  are  almost  invariably  the  products  of  high 
temperatures  and  have  been  formed  by  reaction  and  sometimes 
by  polymerization  of  certain  members  of  the  less  complicated 
open  chain  series.  They  are  difficult  to  isolate  and  indentify 
and  are  only  mentioned  as  connecting  links  between  the  more 
important  and  better  known  series  of  hydrocarbons. 

Members  of  another  series,  which  deserve  mention,  known  as 
the  camphan  group  of  terpenes,  having  the  general  formula 
CnH2n_4,  are  also  found  in  tars  and  the  bitumens  of  an  asphaltic 
nature.  Camphene  is  a  typical  member  of  this  series  and  may 
be  graphically  expressed  as  follows: 


HYDROCARBONS  1 29 

CH2  -  CH CH 

I 
CHQ-  C  •  CH. 


CH2  -  C CH 


CH 


Hydrocarbon  Derivatives.  —  As  has  been  noted,  oxygen,  sul- 
phur and  nitrogen  derivatives  of  the  hydrocarbons  are  found 
in  bituminous  materials,  but  usually  in  far  smaller  quantities 
than  the  hydrocarbons  themselves.  Their  effect  upon  the  phys- 
ical properties  of  the  bitumens  is  often  of  considerable  impor- 
tance. The  elements  oxygen  and  sulphur  react  with  many  of 
the  hydrocarbons,  especially  at  high  temperatures,  to  form  other 
compounds,  and  this  fact  is  made  use  of  in  the  preparation  of 
certain  classes  of  road  binders.  Somewhat  similar  reactions 
have  probably  been  the  direct  cause  of  the  natural  formation 
of  the  solid  native  bitumens. 

Oxygen  derivatives  of  the  hydrocarbons  are  known  chemi- 
cally as  alcohols,  ethers,  aldehydes,  ketones  and  acids,  and  the 
sulphur  and  nitrogen  compounds  are  usually  considered  as  direct 
derivatives  of  these  oxygen  compounds.  Some  of  these  products 
will  be  considered  in  connection  with  the  individual  classes  of 
bitumens  in  the  following  chapters.  They  are  so  numerous  that 
it  is  hardly  practicable  to  even  classify  them  in  this  chapter. 

Summary  and  Conclusions.  —  While  this  chapter  may  to  the 
casual  reader  appear  somewhat  involved  and  irrelevant,  it  will  be 
found  in  later  portions  of  this  book  that  the  brief  description  of 
the  hydrocarbons  as  given  above  will  prove  of  considerable  serv- 
ice in  classifying  the  various  forms  of  bituminous  road  materials. 
The  more  important  hydrocarbon  series  which  have  been  men- 
tioned are  summarized  in  the  following  table.  For  more  de- 
tailed information  than  that  given  in  this  chapter,  reference 
should  be  made  to  any  of  the  standard  textbooks  on  organic 
chemistry. 


130 


DUST  PREVENTIVES  AND   ROAD  BINDERS 


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CHAPTER  VII. 

BITUMENS  EMPLOYED   AS  DUST  PREVENTIVES  AND   ROAD 

BINDERS. 

VARIOUS  types  of  bitumens  employed  as  dust  preventives  and 
road  binders  have  already  been  mentioned  in  Chapter  II,  but 
before  taking  up  the  different  classes  individually,  it  may  be 
well  to  consider  their  further  classification  with  relation  to  one 
another,  their  origin  and  methods  of  formation.  The  word 
bitumen  is  a  generic  term  that  has  been  made  to  include  a  great 
variety  of  substances  and  much  confusion  has  arisen  as  to  just 
what  the  word  signifies.  Any  definition  which  may  at  the 
present  time  be  advanced  is  a  purely  arbitrary  one.  A  slight 
modification  of  Richardson's  definition  of  native  bitumens  has, 
however,  seemed  to  the  author  to  convey  more  nearly  a  correct 
idea  of  the  term  than  any  other.  According  to  this  definition, 
bitumens  may  be  described  as  consisting  of  a  mixture  of  native 
or  pyrogenetic  hydrocarbons  and  their  derivatives,  which  may 
be  gaseous,  liquid,  a  viscous  liquid  or  solid,  but  if  solid,  melting 
more  or  less  readily  upon  the  application  of  heat  and  soluble  in 
chloroform,  carbon  bisulphide  and  similar  solvents.  Mineral 
organic  compounds  which  are  not  soluble  to  any  extent  in  these 
solvents,  but  which,  upon  being  subjected  to  the  process  of 
destructive  distillation,  give  rise  to  the  bitumens,  are  termed 
pyro-bitumens.  Bitumens  themselves  may  be  divided  into  two 
main  classes,  native  and  artificial.  The  former,  as  their  name 
implies,  occur  in  nature,  while  the  latter  are  produced  by  the 
destructive  distillation  of  either  pyro-bitumens  or  the  bitumens 
themselves.  In  certain  cases,  it  is  impossible  to  make  a  sharp 
distinction  between  native  bitumens,  artificial  bitumens  and 
pyro-bitumens,  as  they  often  merge  into  one  another.  Taken 
broadly,  however,  this  classification  is  a  most  convenient  one 


132  DUST   PREVENTIVES   AND    ROAD    BINDERS 

to  follow  when  considering  the  individual  types  of  bituminous 
materials. 

Native  Bitumens.  —  According  to  Richardson,  "Native  bitu- 
mens consist  of  a  mixture  of  native  hydrocarbons  and  their 
derivatives,  which  may  be  gaseous,  liquid,  a  viscous  liquid  or 
solid,  but  if  solid,  melting  more  or  less  readily  on  the  application 
of  heat,  and  soluble  in  turpentine,  chloroform,  bisulphide  of 
carbon,  similar  solvents,  and  in  the  malthas  or  heavy  asphaltic 
oils."  Natural  gas,  petroleum,  maltha,  ozocerite,  hatchettite, 
fossil  resins,  numerous  varieties  of  asphalt,  glance  pitch,  manjak, 
gilsonite  and  grahamite  may  all  be  classed  as  native  bitumens, 
although  some  varieties  of  grahamite  closely  approach  the 
pyro-bitumens  in  characteristics.  If  the  liquid  native  bitumens 
or  petroleums  are  subjected  to  the  process  of  distillation  or 
evaporation  residues  are  obtained  which  can  be  considered 
as  artificial  bitumens  only,  although  in  certain  respects  they 
may  resemble  some  of  the  native  bitumens.  The  fact  that 
such  a  distinction  is  not  clearly  understood  has  been  the  cause  of 
much  confusion  among  road  engineers  in  regard  to  the  com- 
position of  certain  asphaltic  road  oils  and  residual  pitches 
which  have  come  under  their  notice.  In  nature  petroleums 
may  be  and  undoubtedly  have  been  subjected  to  the  process  of 
distillation  or  evaporation  with  the  production  of  semisolid 
and  solid  bitumens.  The  character  of  the  original  oil  as  well 
as  the  natural  conditions  attending  this  transformation  have 
undoubtedly  produced  the  various  types  of  solid  native  bitumens 
mentioned  above.  Thus  paraffin  petroleums  or  those  composed 
largely  of  CnH2n+2  hydrocarbons  are  the  source  from  which 
ozocerite  and  hatchettite  have  been  produced.  Cyclic  oils  con- 
taining principally  CwH2;i,  CnH2n+2,  CnH2n_4,  etc.,  hydrocarbons 
both  saturated  and  unsaturated  have  given  rise  to  the  asphalts 
and  other  closely  related  bitumens.  The  malthas  hold  an  in- 
termediate position  between  the  petroleums  and  these  solid 
bitumens. 

A  number  of  theories  have  been  advanced  as  to  the  origin  of 
native  bitumens  and  no  one  theory  has  as  yet  been  generally 


BITUMENS    EMPLOYED   AS    DUST   PREVENTIVES  133 

accepted.  In  a  recent  treatise  *  Peckham  states  that  "generally 
speaking,  the  theories  advanced  fall  into  three  classes,  embrac- 
ing those  which  regard  bitumen  as  a  distillate  produced  by 
natural  causes,  those  which  regard  bitumen  as  the  product  of  a 
peculiar  decomposition  of  organic  matter  within  the  formations 
in  which  the  organic  matter  is  enclosed,  making  the  bitumen  in 
a  sense  indigenous  to  the  rocks  in  which  it  is  found,  and  those 
which  regard  bitumen  as  a  product  of  chemical  reaction,  the 
latter  class  being  subdivided  into  those  which  regard  bitumen 
as  a  product  of  chemical  change  in  natural  substances  of  which 
carbon  and  hydrogen  are  constituents,  and  those  which  advo- 
cate a  purely  chemical  reaction  between  purely  mineral  or 
inorganic  materials." 

After  a  somewhat  exhaustive  review  of  the  available  data  con- 
cerning this  subject  and  the  experimental  work  of  many  investi1 
gators,  he  strongly  advocates  the  first  theory,  which  is  perhaps 
more  satisfactory  than  any  other  single  theory  yet  advanced. 
To  quote  his  summary  of  the  matter:  "Upon  this  hypothesis, 
that  bitumens  are  distillates,  all  of  the  variations  observed  in 
bitumens  of  different  geological  ages  are  easily  explained.  The 
earliest  forms  of  animal  and  vegetable  life  are  admitted  to  have 
been  nearly  destitute  of  nitrogen:  hence  when  these  forms 
accumulated  in  sediments,  which,  borne  down  by  deposits 
above  them,  invaded  an  isothermal  that  admitted  of  their 
distillation,  they  must  have  been  distilled,  in  the  presence  of 
steam,  at  the  lowest  possible  temperature;  they  must  have  been 
distilled  under  a  gradually  increasing  pressure,  the  extent  of 
which  depended  upon  the  porosity  of  the  sediments  above  them, 
up  to  the  surface.  They  must  also  have  been  distilled  under  a 
gradually  increasing  temperature  which  would  have  been  largely 
controlled  by  the  pressure.  While  the  temperature  and  the 
pressure  would  have  in  every  instance  been  the  least  possible, 
with  steam  always  present,  these  physical  conditions  would  on 
account  of  the  varying  porosity  and  consequent  varying  resist- 
ance of  the  overlying  mass  have  produced  very  great  effects  in 

*  Solid  Bitumens,  page  21.     M.  C.  Clark. 


134  DUST   PREVENTIVES   AND    ROAD   BINDERS 

some  instances  and  very  slight  effects  in  others.  As  a  conse- 
quence, we  have  in  natural  bitumens,  as  in  artificial  distillates, 
materials  varying  in  density  from  natural  gas  to  solid  asphaltum. 

"If  these  distillates  proceeded  from  materials  that  would 
yield  paraffine,  these  permanent  and  stable  compounds,  from 
rrlarsh  gas  to  solid  paraffin,  remained  in  the  receptacles  that 
nature  had  provided  for  them  until  they  were  released  by  the 
drill.  If,  however,  the  distillates  proceeded  from  sediments 
of  a  different  geological  age,  containing  animal  and  vegetable 
remains  more  highly  organized,  that  would  yield  different 
series  of  hydrocarbons,  with  compounds  of  nitrogen,  then  a 
very  different  bitumen  would  be  stored  in  these  receptacles. 
Secondary  reactions  would  convert  these  primary  distillates 
into  a  great  variety  of  substances.  The  contents  of  the  original 
reservoirs,  borne  down  and  invaded  by  heat,  might  become 
involved  in  a  second  distillation  at  an  increased  pressure  and 
temperature.  Fractures  of  these  reservoirs  from  excessive 
pressure  might  lead  their  contents  to  the  surface  along  lines  of 
contact  of  strata  or  with  water  containing  sulphates  by  which 
an  originally  pure  hydrocarbon  would  be  converted  into  a 
sulphur  bitumen.  A  nitrohydrocarbon  reaching  the  surface, 
under  these  conditions,  might,  by  the  combined  action  of 
evaporation  and  reaction  with  sulphates,  pass  through  all  the 
varying  degrees  of  density  from  petroleum  to  maltha  and 
become,  finally,  solid  asphaltum,  and  this,  through  the  lapse  of 
time  and  abundance  of  material,  on  a  scale  of  vast  magnitude." 

Artificial  Bitumens.  —  The  artificial  bitumens  may  be  di- 
vided into  two  main  classes  according  to  their  method  of 
formation,  those  produced  by  a  partial  distillation  of  the  bitumens 
themselves  and  those  produced  by  the  destructive  distillation 
of  the  bitumens  and  pyro-bitumens  as  well  as  certain  other  sub- 
stances of  an  organic  nature.  In  the  first  case  two  classes  of 
artificial  bitumens  are  formed  which  are  known  as  distillates 
and  residues.  The  distillates  are  almost  invariably  fluid,  while 
the  residues  may  be  fluid,  semisolid,  or  solid  according  to  the 
extent  to  which  the  process  of  distillation  has  been  carried.  If 


BITUMENS   EMPLOYED  AS   DUST  PREVENTIVES  135 

fluid  they  are  termed  residual  oils  or  tars,  as  the  case  may  be, 
and  if  solid  should  be  called  residual  pitches.  Residual  pitches 
which  have  been  produced  from  asphaltic  and  semiasphaltic 
oils  are,  however,  often  given  the  trade  name  of  asphalt,  which 
is  very  misleading  and  has  caused  much  confusion  among  the 
uninitiated  as  to  what  the  term  asphalt  implies.  This  has  led 
to  the  use  of  the  expression  " asphalt  contents"  of  an  oil,  by 
which  is  meant  the  residual  pitch  of  a  given  consistency  that 
may  be  formed  by  volatilizing  a  sufficient  quantity  of  the  lighter 
constituents  present.  As  will  be  shown  later,  this  term  is  abso- 
lutely erroneous  for  the  reason  that  such  a  residue  is  not,  strictly 
speaking,  an  asphalt  at  all  and  in  many  cases  is  not  even  a 
measure  of  the  residual  contents  of  the  oil,  but  only  of  the  ability 
of  the  oil  to  produce  such  residues  at  high  temperatures. 

Artificial  bitumens  produced  by  destructive  distillation  are 
commonly  known  as  tars.  The  word  tar  is  often  compounded 
with  the  name  of  the  material  which  has  been  subjected  to  the 
process  of  destructive  distillation,  thus  designating  its  origin, 
for  example,  coal-tar,  oil-tar,  wood-tar.  Tars  are  the  liquid 
distillates  obtained  by  cooling  the  gases  produced  by  distilla- 
tion. This  distillation  being  destructive  and  carried  on  until 
little  or  no  more  gases  are  evolved  from  the  material  distilled, 
the  residue  usually  consists  of  carbon  or  coke  together  with  any 
mineral  matter  which  was  originally  present. 

Tars  themselves  are  as  a  rule  distilled  or  refined  before  being 
placed  upon  the  market.  Distillation  is  carried  on  in  a  manner 
quite  similar  to  that  employed  for  oils,  and  distillates  and 
residues  are  produced.  The  distillates  are  oily  liquids  which 
often  precipitate  cry  s  tall  izable  solids  upon  cooling.  The 
residues  as  in  the  case  of  oils  may  be  fluid,  semisolid  or  solid. 
Fluid  residues  from  such  distillation  are  known  as  refined  tars 
and  the  semisolid  and  solid  as  soft  or  hard  pitches  according  to 
their  degree  of  hardness.  Distillates  and  residues  from  tars 
are  quite  different  in  character  from  petroleum  distillates  and 
residues.  They  are  composed  mainly  of  CnH2n_6,  CnH2n_12, 
and  CJH2n_18  hydrocarbons  and  their  derivatives. 


136  DUST  PREVENTIVES   AND   ROAD   BINDERS 

In  all  cases,  however,  the  distillates  may  be  said  to  exhibit 
little  or  no  binding  qualities  and  can,  therefore,  never  be  em- 
ployed as  road  binders.  They  have  been  used  to  a  slight 
extent  as  dust  preventives,  but  are  usually  unsatisfactory  for 
even  this  purpose,  as  they  produce  a  slippery,  greasy  mud  in 
rainy  weather.  The  residues  invariably  retain  the  true  binding 
base  of  the  oil  or  tar  if  any  was  originally  present,  and  when 
brought  to  proper  consistency,  represent  that  base  themselves. 
If  distillation  is  carried  on  so  that  none  of  the  individual  con- 
stituents of  the  original  oil  or  tar  are  chemically  altered,  a 
mechanical  separation  only  will  be  effected  and  the  distillation 
is  said  to  be  a  purely  fractional  operation.  Where  some  of  the 
chemical  constituents  are  broken  down  into  other  compounds 
and  chemical  reactions  are  known  to  take  place,  due  to  the  high 
temperature  employed,  the  resulting  residue  is  said  to  be 
cracked.  In  the  former  case  the  residue  of  course  more  nearly 
partakes  of  the  nature  of  the  original  oil  or  tar  than  in  the 
latter.  If  this  cracking  is  carried  beyond  a  certain  point,  the 
residue  is  apt  to  be  seriously  injured  for  road  purposes,  and  if 
carried  to  its  ultimate  conclusion,  results  in  destructive  distilla- 
tion with  the  formation  of  a  tar  distillate  and  coke  residue. 

In  order  to  carry  on  distillation  to  the  greatest  possible  extent 
without  cracking,  recourse  is  often  had  to  the  use  of  reduced 
pressure,  and  the  material  distilled  under  a  partial  vacuum. 
By  this  means  the  boiling  points  of  all  of  the  constituents  are 
lowered,  and  many  which  would  under  ordinary  conditions  break 
down  or  crack  at  their  normal  boiling  point,  pass  over  unaltered 
and  are  collected  in  the  distillate.  Superheated  steam  is  also 
employed  to  some  extent  as  a  mechanical  carrying  agent  for 
the  heavy  oil  vapors,  which,  if  not  removed,  immediately  after 
formation  are  apt  to  be  cracked  by  overheating.  These 
methods  will  be  further  described  under  the  technical  prepara- 
tion of  various  types  of  bituminous  road  materials. 

Pyro-Bitumens.  —  As  has  been  stated,  pyro-bitumens  are 
mineral  organic  substances  which  are  indifferent  to  the  solvents 
for  the  bitumens,  but  which  upon  being  subjected  to  destructive 


BITUMENS    EMPLOYED   AS   DUST  PREVENTIVES  137 

distillation  give  rise  to  the  formation  of  artificial  bitumens. 
They  are  as  a  class  hard  substances,  which  do  not  melt  readily 
upon  the  application  of  heat.  According  to  Richardson,  they 
may  be  divided  into  two  classes,  those  derived  from  petroleum 
and  those  derived  from  direct  metamorphoses  of  vegetable 
growth.  The  former  are  sometimes  called  asphaltic  coals  to 
distinguish  them  from  the  coals  of  direct  vegetable  origin. 
The  minerals  albertite  nigrite,  wurtzelite  and  certain  varieties 
of  grahamite  constitute  the  asphaltic  coals,  while  peat,  lignite, 
bituminous  and  semibituminous  coals,  and  bituminous  shales 
and  schists  compose  the  latter  class.  Certain  of  these  materials 
yield,  upon  destructive  distillation,  distillates  quite  similar  to 
some  of  the  native  bitumens.  The  majority,  however,  yield 
tars  which  are  quite  unlike  any  of  the  native  bitumens.  The 
manner  in  which  the  distillation  is  carried  on  as  well  as  the 
temperatures  employed  of  course  govern  to  a  great  extent  the 
nature  of  the  artificial  bitumen  produced. 

Classification  of  Bituminous  Materials.  —  In  the  following 
tabular  arrangement  of  bituminous  materials,  Richardson's 
classification  of  the  native  bitumens  and  pyro-bitumens  has 
been  closely  followed  by  the  author,  as  representing  the  views 
of  one  of  the  highest  authorities  on  the  subject.  The  artificial 
bitumens  have  been  classified  in  such  a  way  as  to  separate  the 
road  binding  materials  from  those  which  have  no  road  binding 
qualities,  and  in  both  the  native  and  artificial  bitumens  those 
of  most  importance  from  the  standpoint  of  road  treatment  and 
road  construction  have  been  printed  in  capitals. 

BITUMINOUS   MATERIALS. 
I.    NATIVE   BITUMENS. 

(a).  Gases. 

1.  Marsh  gas.     Formed  by  the  decomposition  of  vege- 
table matter  under  water. 

2.  Natural  gas.     Forrned  under  similar  conditions  to  pe- 
troleum and  often  accompanying  it. 


138  DUST  PREVENTIVES  AND   ROAD   BINDERS 

(b).  Petroleums. 

1.  Paraffin  oils..     Consisting  principally  of  C^H2n+2   hy- 
drocarbons and  rich  in  solid  paraffins.     Of  little  value 
as  dust  preventives  and  having  practically  no  binding 
value. 

2.  CYCLIC  OILS  (Asphaltic).    Consisting  principally  of  poly- 
methylene  hydrocarbons  of  the  series  CnH2^,  CnH2n_2, 
CnH2n_4,  etc.,  together  with  a  certain  amount  of   un- 
saturated  hydrocarbons   and   their   derivatives;   excel- 
lent  dust   preventives   and  possessing,   or   capable   of 
developing  under  service  conditions,  considerable  bind- 
ing value. 

3.  SEMIASPHALTIC  OILS.     Consisting  mainly  of  a  mixture 
of   paraffin  hydrocarbons  and   stable   polymethylenes ; 
holding  an  intermediate  position  between  the  paraffin 
and  asphaltic  oils;  good  dust  preventives,  but  rather 
poor  road  binders  unless  properly  refined. 

(c).  MALTHAS. 

i.  Transition  products  between  petroleum  and  asphalt, 
originating  from  polymethylene  oils;  often  found  im- 
pregnating porous  sandstones  and  limestones,  the  indi- 
vidual particles  of  which  are  thus  bound  together, 
forming  in  many  cases  excellent  road  surfacing  mate- 
rials. 

(d).  Solids.     (Commonly  classified  as  minerals.) 

1.  Paraffin  substances  such  as  ozocerite,  hatchettite,  etc. 
Resembling  paraffin  wax  and  having  no  commercial 
importance  as  road  binders. 

2.  Amber  and  fossil  resins.     Consisting  largely  of  unsat- 
urated  cyclic  hydrocarbons  such  as  the  terpenes. 

3.  ASPHALTIC  SUBSTANCES.     Originating  in  polymethylene 
petroleums,  the  more  volatile  hydrocarbons  and  prob- 
ably many  of  the  less  volatile  consisting  of   complex 
unsaturated  compounds;  many  of  them  excellent  road 
binders  when  cut  with  a  suitable  fluxing  agent,  but  of 


BITUMENS   EMPLOYED   AS   DUST  PREVENTIVES          139 

no  value  for  this  purpose  when  in  their  natural  condi- 
tion owing  to  their  brittleness;  among  the  most  impor- 
tant members  may  be  mentioned  the  following  types 
which  at  the  present  time  have  not  been  satisfactorily 
denned  as  to  differences  in  composition  and  physical 
properties:  asphalts  (such  as  Trinidad,  Bermudez, 
California,  Cuba,  etc.),  glance  pitch,  Manjak,  Gilsonite, 
Grahamite. 

II.    PYRO-BITUMENS. 

(a).  Derived  from  petroleum  (asphaltic  coals). 

1.  Albertite. 

2.  Wurtzilite. 

(b).  Derived  from  direct  metamorphosis  of  vegetable  matter. 

1.  Peat. 

2.  Lignite. 

3.  BITUMINOUS  COAL.     Source  of  coal  tar. 

4.  Semi-bituminous  coal.     Approaching  anthracite,  which 
is  not  strictly  speaking  a  pyro-bitumen. 

(c).    Bituminous  schists  and  shales. 

III.    ARTIFICIAL  BITUMENS. 

(a).  Derived  from  the  destructive  distillation  of  bitumens  and 
pyro-bitumens,  mainly  petroleum  and  bituminous  coal, 
and  known  as  tars. 

1.  Oil  tars.  —  WATER  GAS  TARS.     Thin  oily  liquids  mixed 
with  considerable  quantities  of  water;  consisting  prin- 
cipally of  unsaturated  cyclic  hydrocarbons  of  the  CnH2n_6, 
CnH.2n-i2  and  CnH2^_18  series  together  with  saturated 
compounds;  serviceable  as  dust  preventives  but  of  little 
or  no  value  as  road  binders  in  their  natural  state. 

2.  COAL  TARS.     Viscous  sticky  liquids  mixed  with  a  certain 
amount  of  water;  consisting  mainly  of  CnH2n_6,  CnH2ri_12 
and  CnH2n_18  hydrocarbons  with    their  oxygen  deriva- 
tives known  as  phenols,  cresols,  etc.,  together  with  sul- 


I4O  DUST   PREVENTIVES   AND    ROAD    BINDERS 

phur  and  nitrogen  derivatives;  often  excellent  dust 
preventives  but  unsatisfactory  as  road  binders  in  their 
crude  state. 

(b).  Derived  from  the  fractional  distillation  of  petroleum. 

1.  Distillates.    Chemically  identical  with  portions  of  the 
original  oil  unless  cracking  has  occurred  during  distil- 
lation; having  no  binding  value  and    being  unsuitable 
for  use  as  dust  preventives.   Among  this  class  of  materials 
may  be  mentioned  petrolic  ether,  benzine,  kerosene  or 
illuminating  oil,  and  some  lubricating  oils. 

2.  RESIDUES.    Varying  in  nature  according  to  the  character 
of  the  original  oil  and  the  extent  to  which  distillation  has 
been  carried,  but  composed  mainly  of  unaltered  por- 
tions of  the  original  oil   unless  cracking  has  been  re- 
sorted to. 

(aa).  Reduced  oils. 

Fluid  products  from  which  only  the  most  vol- 
atile portions  have  been  removed;  but  little  used 
in  the  treatment  of  roads. 

(bb).  RESIDUAL  OILS. 

Viscous  products  resulting  from  the  removal  of  all 
volatiles  to  and  including  the  lubricating  oils;  of 
little  value  as  dust  preventives  and  of  no  value  as 
road  binders  if  derived  from  paraffin  petrole- 
ums; if  produced  from  semiasphaltic  or  asphaltic 
oils  their  value  for  road  purposes  is  proportional 
to  their  asphaltic  characteristics  and  consistency. 
Often  valuable  fluxing  agents  for  solid  bitumens 
too  brittle  to  be  used  in  their  original  condition. 

(cc).  RESIDUAL  PITCHES.  Semisolid  and  solid  prod- 
ucts sometimes  called  artificial  or  oil  asphalts. 
The  softer  varieties  give  excellent  results  as  road 
binders  if  of  asphaltic  oil  origin.  Sometimes  these 
products  are  blown  with  air  while  hot,  which  pro- 
duces a  cheesy  non-ductile  residue  of  inferior 


BITUMENS   EMPLOYED    A.S   DUST   PREVENTIVES  141 

road  building  qualities  if  the  blowing  process  is 
carried  too  far.  In  order  to  make  the  harder 
residual  pitches  suitable  for  road  work,  it  is  nec- 
essary to  cut  them  with  a  fluxing  oil  as  in  the 
case  of  native  asphalts. 
(c).  Derived  from  the  fractional  distillation  of  tars. 

1.  Distillates   chemically   identical  with  portions  of  the 
original  tar.     Of  no  importance  as  dust  preventives  and 
of  no  value  as  binders.     Among  the  distillates  may  be 
mentioned  water,  light  oils,  carbolic  oils,  creosote  oils  and 
anthracene  oils.     Solid  substances  such  as  naphthalene 
and  anthracene  crystallize  out  of  some  of  these  distillates. 
The  creosote  and  anthracene  oils  while  possessing  no 
binding   value    themselves   serve   as   excellent   fluxing 
mediums  for  the  hard  pitches  which  exhibit  a   true 
binding  value. 

2.  RESIDUES.     Varying  in  nature  according  to  the  char- 
acter of  the  original  tar  and  the  extent  to  which  dis- 
tillation has    been   carried;    composed   mainly   of   the 
unaltered  heavier  products  of  the  original  tar. 

(aa).  DEHYDRATED  TARS. 

Fluid  products  from  which  only  the  water  has 
been  removed.  If  derived  from  oil  they  show 
little  road  binding  characteristics,  but  are  good 
dust  preventives;  if  from  coal  they  are  often  of 
considerable  value  both  as  dust  preventives  and 
semipermanent  binders. 

(bb).  REFINED  TARS. 

Viscous  products  holding  an  intermediate  posi- 
tion between  the  dehydrated  tars  and  the  pitches. 
If  properly  prepared  either  from  water  gas  or 
coal  tar  they  are  of  considerable  value  as  road 
binders.  If,  however,  they  contain  large  quan- 
tities of  crystallizable  solids  and  free  carbon 
their  value  for  road  purposes  is  greatly  lessened. 


142  DUST  PREVENTIVES   AND   ROAD  BINDERS 

(cc).   PITCHES. 

Semisolid  and  solid  residues,  the  softer  varieties 
being  adapted  for  use  as  binders  in  road  con- 
struction.    The  harder  pitches   are   too   brittle 
for  road  purposes  and  have  to  be  fluxed  with 
lighter  tar  products  before  they  can  be  so  used. 
Summary  and  Conclusions. —  In    this     chapter    bituminous 
materials,  including  native  bitumens,  pyro-bitumens  and  arti- 
ficial bitumens,  have  been  described  and  classified  with  special 
reference  to  the  subject  of  this  book.     It  is  realized  that  the 
classification  is  not  complete,  inasmuch  as  the  artificial  bitumens 
obtainable  from  such  pyro-bitumens  as  peat,  lignite,  bituminous 
shales,  etc.,  and  from  wood,  bone  and  other  organic  substances, 
have  not  been  included.     As  such  materials,  however,  are  of 
very  slight  importance  so  far  as  dust  preventives  and  road 
binders  are  concerned,  it  has  been  thought  unnecessary  to  con- 
sider them  in  this  classification. 


OF   THE 

UNIVERSITY 

OF 


CHAPTER  VIII. 
PETROLEUM  AND   PETROLEUM  PRODUCTS. 

PETROLEUMS,  rock  oils  or  mineral  oils  are  fluid  native  bitumens 
widely  distributed  over  the  earth,  the  largest  quantities  being 
found  in  the  United  States  and  Russia.  Petroleums  differ 
widely  in  characteristics  according  to  the  locality  from  which 
they  are  derived,  and  while  those  occurring  in  the  United  States 
will  be  mainly  considered  in  this  chapter,  it  should  be  under- 
stood that  remarks  relative  to  their  value  as  dust  preventives 
and  road  binders  are  also  applicable  to  oils  from  many  other 
countries,  as  nearly  all  of  the  important  types  are  here  repre- 
sented. 

The  petroleum  industry  in  this  country  starting  with  the 
production  of  about  two  thousand  barrels  in  1859,  valued  at 
$32,000,  has  in  the  period  of  fifty  years  assumed  enormous 
proportions,  the  total  output  for  1908  alone  being  nearly  180,- 
000,000  barrels  or  7,560,000,000  gallons,  with  a  total  value  of 
nearly  $130,000,000.  This  represents  about  63  per  cent  of  the 
world's  total  output  for  1908. 

According  to  Day,*  "  In  all  nearly  two  billion  barrels  have 
been  produced  in  forty-nine  years,  worth  one  and  three-fourths 
billion  dollars.  This  is  more  than  half  the  value  of  all  our  gold 
and  more  than  the  entire  value  of  our  silver  produced  in  twice 
as  many  years.  The  value  of  the  petroleum  in  1908  exceeded 
the  value  of  the.  gold  and  silver  combined  by  over  two  million 
dollars."  The  following  table  gives  the  total  quantity  and 
value  of  crude  petroleum  produced  in  the  United  States  and  the 
average  price  per  barrel  of  forty- two  gallons  in  1907  and  1908 
by  states. 

*  "The  Production  of  Petroleum  in  1908."  "  Mineral  Resources  of  the  United 
States,  Calendar  Year  1908."  U.  S.  Geological  Survey. 


144 


DUST   PREVENTIVES  AND    ROAD   BINDERS 


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PETROLEUM  AND  PETROLEUM  PRODUCTS      145 

According  to  physical  and  chemical  properties  as  well  as  to 
geological  formation,  the  petroleums  of  the  United  States  may 
be  classified  under  a  number  of  fields.  The  location  from  which 
an  oil  is  obtained  may,  therefore,  be  considered  an  index  of  its 
general  character,  and  so  of  its  value  as  a  dust  preventive  or 
road  binder.  The  custom  of  grouping  oils  according  to  the 
quality  has  become  quite  general  in  the  trade.  A  number  of 
terms,  such  as  " Pennsylvania  grade,"  "Lima  grade"  and 
"Kansas  grade,"  are  in  common  use,  the  distinction  being  based 
both  on  the  percentage  of  sulphur  and  on  the  proportion  of 
artificial  asphalt  and  paraffin  wax  to  the  illuminating  oil  obtain- 
able from  the  crude. 

The  value  of  an  oil  as  a  permanent  dust  preventive  and  road 
binder  lies  in  the  quality  and  quantity  of  high  binding  bitumi- 
nous base  retained  by  the  road  surface  after  evaporation  of  the 
more  volatile  constituents.  The  bases  present  in  petroleums 
vary  from  the  almost  pure  paraffin  to  the  almost  pure  asphalt, 
many  being  a  mixture  of  the  two.  While  the  paraffin  oils  are 
of  much  more  value  than  the  asphaltic  from  a  commercial  point 
of  view,  the  opposite  is  true  from  the  standpoint  of  dust  sup- 
pression. A  wholly  paraffin  oil  is  of  value  only  as  a  temporary 
binder  or  dust  layer,  while  an  asphaltic  oil,  owing  to  the  character 
of  the  base  contained,  ranks  very  favorably  with  other  mate- 
rials as  a  permanent  binder.  Petroleum  is  a  mixture  of  a  great 
number  of  hydrocarbons  together  with  comparatively  small 
quantities  of  sulphuretted,  nitrogenized,  and  oxygenated  com- 
pounds. The  approximate  composition  of  crude  petroleum  is 
ordinarily  determined  by  distillation,  but  a  knowledge  of  the 
residuums  left  after  distillation  is  of  far  more  value  from  the 
standpoint  of  road  treatment.  Considerable  attention  has  been 
paid  to  these  residuums,  as  well  as  to  the  characteristics  shown 
by  oils  from  the  various  fields. 

Oil  Fields  in  the  United  States.  —  There  are  six  distinct  oil 
fields  in  the  United  States,  known  as  (i)  the  Appalachian  Field, 
(2)  the  Lima-Indiana  or  Ohio-Indiana  Field,  (3)  the  Illinois 
Field  (recently  classified  as  such),  (4)  the  Mid-Continent  Field, 


146 


DUST  PREVENTIVES   AND    ROAD   BINDERS 


(5)  the  Gulf  Field  and  (6)  the  California  Field.  Small  quan- 
tities of  oil  have  also  been  found  in  Wyoming,  Colorado,  Missouri, 
Michigan  and  Utah  and  occur  in  Arkansas,  Montana,  Washing- 
ton, Oregon,  Idaho  and  Nevada.  The  following  table*  gives 
the  production  of  crude  petroleum  in  barrels,  in  the  United 
States  for  the  years  1903  to  1908,  inclusive,  by  fields. 


Field. 

1903. 

1904. 

1905- 

Appalachian 

•j  I  r  r8  248 

31  408  ^67 

2Q  366  060 

Lima-Indiana 

24,080,264 

24,689,184 

22,294  171 

Illinois            .                

181,084 

Mid-Continent  

1.1:72,081? 

6,186,629 

12,1:31;,  777 

Gulf  

18,^71,383 

24,631,269 

36x26,323 

California 

24  382  472 

2Q,64Q  434 

33  427  473 

Other                              

4QC,88<; 

fl  t  877 

38?  7Q2 

100,461,337 

117,080,960 

134,717,5s0 

Field. 

1906. 

1907. 

1908. 

Appalachian 

27  741  472 

2C  342  137 

24  Q4?  c;i7 

Lima-Indiana 

17  ,CC4,66l 

13,1  2  1,094 

10,032  30? 

Illinois     

4,3Q7,ot;o 

24,28l,Q73 

33,68=1,106 

Mid-Continent  

22,838,^3 

46,846,267 

48,323,810 

Gulf  

2o,i?27,s;2o 

16,410,299 

17,318,330 

California 

33  008  ?o8 

30  748,37? 

44  8?4  737 

Other 

336,082 

34=;,IQO 

412  674 

126,493,936 

166,095,335 

177,572,479 

Appalachian  Field.  —  The  Appalachian  field  extends  from  west- 
ern New  York  in  a  general  southwesterly  direction  along  the 
western  side  of  the  Allegheny  Mountains,  through  Pennsyl- 
vania, eastern  Ohio,  the  northwestern  part  of  West  Virginia  into 
eastern  Kentucky  and  Tennessee.  In  parts  of  Ohio,  Kentucky 
and  Tennessee,  the  oils  vary  in  character  and  some  closely  re- 
semble the  products  of  the  Lima-Indiana  field.  The  oils  of  the 
Appalachian  field  as  a  class  are  practically  free  from  sulphur 
and  asphaltic  hydrocarbons,  but  rich  in  paraffins,  both  liquid 
and  solid.  They  are  the  most  valuable  of  all  crude  oils  as  they 

*  Report  of  Geological  Survey,  loc.  cit. 


PETROLEUM  AND  PETROLEUM  PRODUCTS      147 

yield  the  largest  percentage  of  gasoline  and  illuminating  oils. 
During  the  year  1908,  this  field  produced  about  14  per  cent  of 
the  total  output  of  oil  in  the  United  States,  the  crude  material 
selling  for  about  $1.76  per  barrel.  The  Pennsylvania  oils  in 
particular  have  been  closely  studied  by  Mayberry,  Young, 
Richardson  and  others  as  being  representative  examples  of  the 
Appalachian  field.  According  to  Richardson,  "The  paraffin  pe- 
troleums of  the  Appalachian  field  consist  of  small  amounts  of 
monocyclic  aromatic  and  polymethylene  hydrocarbons,  which 
have  been  separated  in  such  a  degree  of  purity  as  to  be  identified 
definitely;  of  minute  traces  of  sulphur  and  nitrogen  compounds 
and  predominatingly,  of  paraffin  hydrocarbons  from  isobutane 
(C4H10)  to  C35H72,  the  members  above  14  being  solids  at  ordinary 
temperatures.  Polycyclic  hydrocarbons  of  the  CnH2rt  series  are 
also  present  in  very  considerable  amounts,  from  C21  to  C26,  the 
constitution  of  which  is  not  understood  but  which  are  quite 
different  from  the  hydrocarbons  of  the  same  relation  of  carbon 
and  hydrogen  found  in  asphaltic  oils,  and  have  no  relation  to 
the  ethylene  or  olefine  series.  Polycyclic  hydrocarbons  of  the 
CnH2n_2  series  are  also  present  in  the  fractions  boiling  above  290° 
at  50  mm.  The  two  latter  classes  of  hydrocarbons  are  worthy 
of  careful  study.  They  are  saturated,  in  that  they  are  not  acted 
upon  by  strong  sulphuric  acid,  and  are  all  sharply  differenti- 
ated from  the  hydrocarbons  of  the  asphaltic  petroleums  of 
California  by  their  physical  properties." 

The  characteristics  of  dense  residuums  obtained  from  these 
oils  are  represented  by  the  following  results  obtained  from  an 
examination  of  a  Pennsylvania  oil  residuum  by  Richardson, 
who  has  made  a  particular  study  of  residuums  as  of  interest  in 
the  paving  industry 

(a)     PENNSYLVANIA  OIL  RESIDUUM.* 
PHYSICAL  PROPERTIES. 

Specific  gravity,  2^/25°  C o.  9202 

Flash,  degrees  C 186° 

*  This  and  other  analyses  marked  (a)  are  taken  from  VI  Congresso  Inter- 
nazionale  di  chimica  applicata,  Roma,  1906.  Communicazione  fatta  nella  Sezione 
IV.  —  A.  (Industrie  dei  prodotti  organici). 


148  DUST  PREVENTIVES    AND    ROAD   BINDERS 

CHEMICAL  CHARACTERISTICS. 

Loss  at  160°,  7  hours 5.3% 

Character  of  residue Soft. 

Loss  at  205°,  7  hours  (fresh  sample) 14-2% 

Character  of  residue Soft. 

Character  of  residue  to  constant  weight Brittle  pitch 

Bitumen  soluble  in  CS2,  air  temperature 99.8% 

Organic  matter,  insoluble 0.2% 

Inorganic  or  mineral  matter 0.0% 

100.  o 

Bitumen  insoluble  in  88°  B.  naphtha,  air  temperature 4-3% 

Per  cent  of  soluble  bitumen  removed  by  H2SO4 21.9% 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons 74.8% 

Per  cent  of  solid  paraffin n .0% 

Fixed  carbons 3 .  o% 

The  brittle  pitch  noted  above  is  probably  formed  by  molec- 
ular condensation  at  high  temperatures,  which  will  be  dis- 
cussed later  in  this  chapter,  and  was  not  present  in  the  original 
oil.  It  will  be  noted  that  this  residue  contains  a  much  higher 
percentage  of  solid  paraffin  than  the  oil  residues  from  any  but 
the  Lima-Indiana  oils.  Such  oils  are  unsuited  for  road  pur- 
poses either  in  their  crude  or  refined  state,  except  as  fluxes  for 
certain  solid  bitumens  of  an  asphaltic  nature. 

Lima-Indiana  Field.  —  This  field  includes  the  northwestern 
part  of  Ohio  and  middle  Indiana.  At  one  time  the  Illinois 
field  was  included,  but  it  has  since  been  shown  to  constitute 
a  field  by  itself.  The  Lima-Indiana  oils,  although  classed  as 
paraffin  petroleums,  are  denser  than  those  obtained  from  the 
Appalachian  field,  and  contain  much  larger  quantities  of  sulphur 
compounds,  which  give  them  a  disagreeable  odor  and  make  a 
special  treatment  necessary  while  being  refined.  They  pro- 
duce less  illuminating  oils  than  the  Appalachian  petroleums  and 
are,  therefore,  less  valuable,  the  price  per  barrel  during  1908  being 
about  one  dollar.  The  output  for  that  year  amounted  to  about 
5.6  per  cent  of  the  total  oils  produced  in  the  United  States. 

Considerable  quantities  of  solid  paraffins  are  found  in  the 
Lima-Indiana  field,  and  certain  asphaltic  hydrocarbons  which 
are  not  present  in  the  Appalachian  oils.  Saturated  CnH2n  and 
CnH2/l_2  hydrocarbons  of  higher  boiling  point  begin  at  a  much 


PETROLEUM  AND  PETROLEUM  PRODUCTS       149 

lower  number  of  carbon  atoms  than  in  the  Appalachian  oils,  and 
hydrocarbons  of  the  series  CnH2n_4  are  found  which  do  not  exist 
in  the  latter.  Larger  amounts  of  naphthenes  and  unsaturated 
hydrocarbons  are  also  found.  The  characteristics  of  a  typical 
dense  Ohio  oil  residuum  are  shown  in  the  following  table: 

(a)     OHIO    OIL    RESIDUUM. 
PHYSICAL  PROPERTIES. 

Specific  gravity,  2$°/2$°  C 0.9318 

Flash,  degrees  C 224° 

CHEMICAL  CHARACTERISTICS. 

Loss,   160°  C.,  7  hours 0.3% 

Character  of  residue Soft. 

Loss,  200°  C.,  7  hours  (fresh  sample) 7 . 4% 

Character  of  residue Soft. 

Bitumen  soluble  in  CS2,  air  temperature 99 . 4% 

Organic  matter,  insoluble o .  6% 

Inorganic  or  mineral  matter 0.0% 

100.  o 

Bitumen  insoluble  in  88°  B.  naphtha,  air  temperature 3-8% 

Per  cent  of  soluble  bitumen  removed  by  H2SO4 17.0% 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons 83.0% 

Per  cent  of  solid  paraffin 1 1 . 4% 

Fixed  carbon 3 .  7% 

It  will  be  seen  that  this  residuum  is  quite  similar  to  that 
obtained  from  the  Pennsylvania  oil.  Such  products  are,  there- 
fore, of  no  value  as  road  binders. 

Illinois  Field.  —  The  Illinois  field,  being  of  more  recent  devel- 
opment, has  not  received  as  much  study  as  the  two  preceding 
fields.  In  general  the  Illinois  oils  contain  less  sulphur  than  the 
Lima-Indiana  oils,  although  they  vary  within  wide  limits. 
Some  contain  considerable  quantities  of  asphaltic  hydrocarbons 
and  approach  in  character  oils  found  in  the  Gulf  field.  This  is 
also  true  of  certain  Kentucky  oils  which  seem  to  be  closely 
related  to  those  found  in  southern  Illinois.  Both  these  Illinois 
and  Kentucky  oils  have  been  used  to  a  considerable  extent  in 
the  treatment  of  roads.  The  value  of  Illinois  oils  during  1908 
was  considerably  less  than  the  Lima-Indiana  oils,  being  sold  at 
about  sixty-seven  cents  per  barrel,  a  difference  of  thirty-three 
cents.  The  output  for  this  field  in  1908  was  very  large,  represent- 


150  DUST  PREVENTIVES   AND    ROAD    BINDERS 

ing  about  18.8  per  cent  of  the  total  output  of  the  United  States. 
An  examination  of  a  southern  Illinois  oil  residuum,  made  by  the 
author,  showed  it  to  possess  the  following  characteristics : 

ILLINOIS    OIL    RESIDUUM. 
PHYSICAL  PROPERTIES. 

Character Viscous,  slightly  sticky. 

Specific  gravity,  2S°/2$°  C 941 

Flash,  degrees  C 187° 

CHEMICAL  CHARACTERISTICS. 

Loss  1 63°,  5  hours i .  46% 

Character  of  residue Soft. 

Bitumen  soluble  in  CS2,  air  temperature 99.8% 

Bitumen  insoluble  in  86°  naphtha,  air  temperature 5-9% 

Fixed  carbon 4 .  o% 

Mid-Continent  Field.  —  This  field  embraces  southeastern 
Kansas,  the  eastern  part  of  Oklahoma  and  northern  Texas. 
Like  the  Illinois  field,  it  produces  oils  of  very  varied  character, 
but  as  a  rule  denser  than  the  eastern  oils.  Solid  paraffins  are 
present  but  also  considerable  quantities  of  the  CnH2n,CnH2n_2 
and  CrcH2n_4  hydrocarbons.  They  may  be  said  to  contain  a 
semiasphaltic  base  and  for  road  treatment  rank  with  the  south- 
ern Illinois  and  Kentucky  oils  in  value.  In  1908  the  Kansas 
field  produced  more  oil  than  any  of  the  others,  the  output  being 
26.9  per  cent  of  the  total  output  of  the  United  States.  These 
oils  were  lower  in  price  than  any  of  the  others,  being  about 
thirty-nine  cents  per  barrel.  The  characteristics  of  a  Kansas 
oil  residuum  are  shown  in  the  following  table: 

(a)     KANSAS    OIL    RESIDUUM. 
PHYSICAL  PROPERTIES. 

Specific  gravity,  25%5°  C 0.9328 

Flash,  degrees  C 196° 

CHEMICAL  CHARACTERISTICS. 

Loss,  100°  C.,  7  hours 2 . 6% 

Character  of  residue Soft. 

Loss,  200°  C.,  7  hours  (fresh  sample) 5 . 7% 

Character  of  residue Soft. 

Bitumen  insoluble  in  88°  naphtha,  air  temperature 3 . 6% 

Per  cent  of  soluble  bitumen  removed  by  H2SO4 14.4% 

Per  cent  of  solid  paraffins 7 . 8% 

Fixed  carbon 4.  i% 


PETROLEUM  AND  PETROLEUM  PRODUCTS      15 1 

Gulf  Field.  —  Louisiana  and  all  of  Texas  but  the  northern 
portion  are  included  in  this  field.  The  Gulf  oils  contain  a 
much  smaller  percentage  of  solid  paraffins  than  any  of  the 
others  so  far  mentioned,  and  a  greater  percentage  of  unsatu- 
rated  hydrocarbons.  They  are  as  a  class  more  asphaltic  in 
character  and,  therefore,  more  suitable  for  use  as  road  binders. 
Many  of  them  have  a  high  sulphur  content  and  evolve  a  con- 
siderable amount  of  hydrogen  sulphide.  They  are  more  stable 
than  the  truly  asphaltic  oils  and  in  this  respect  are  superior. 
Their  binding  value  is,  however,  less.  They  are  well  suited  for 
fuel  oils  and  yield  valuable  lubricating  oils.  In  1908  the  Gulf 
field  produced  about  9.6  per  cent  of  the  total  oil  output  of  the 
United  States,  and  sold  at  an  average  price  of  a  little  less  than 
sixty  cents  per  barrel. 

The  characteristics  of  a  typical  dense  Gulf  oil  residuum, 
obtained  from  the  Beaumont  district,  are  shown  in  the  following 
table: 

(a)     GULF    OIL    RESIDUUM. 
PHYSICAL  PROPERTIES. 

Specific  gravity  2^/25°  C 0.9735 

Flash,  degrees  C 214° 

CHEMICAL  CHARACTERISTICS. 

Loss,  160°,  7  hours o .  8% 

Character  of  residue Soft. 

Loss,  200°,  7  hours  (fresh  sample) 6. 2% 

Character  of  residue Soft. 

Bitumen  soluble  in  CS2,  air  temperature 99. 6% 

Organic  matter  insoluble o .  4% 

Inorganic  matter o.o 

100.  O 

Bitumen  insoluble  in  88°  naphtha,  air  temperature 4-8% 

Per  cent  of  soluble  bitumen  removed  by  H2SO4 20.9% 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons 79.4% 

Per  cent  of  solid  paraffins i .  7% 

Fixed  carbon 3 . 5% 

California  Field.  —  While  the  petroleums  of  California  con- 
sist mainly  of  asphaltic  hydrocarbons,  their  density  varies 
within  such  wide  limits  that  they  should  properly  speaking  be 
divided  into  two  classes,  light  grade  and  heavy  grade  oils. 
While  paraffin  petroleums  do  occur  to  some  extent,  in  the 


152  DUST   PREVENTIVES    AND    ROAD   BINDERS 

majority  of  oils  from  this  field,  the  solid  paraffins  are  never 
found.  Hydrocarbons  of  the  CnH2n,  CnH2n_2,  C»H2n_4,  CnH2n_8 
have  been  found,  as  have  also  phenols  and  other  aromatic 
hydrocarbons.  Nitrogeneous  bodies  often  occur  to  a  large 
extent  and  sulphur  compounds  are  also  present.  The  princi- 
pal characteristic  of  California  petroleums,  as  differentiating 
them  from  those  of  the  other  fields,  is  that  their  residues 
consist  largely  of  unstable  polycyclic  polymethylenes  and  thus 
closely  resemble  the  native  asphalts  in  character.  Advantage 
has  been  taken  of  this  fact  for  the  purpose  of  manufacturing 
artificial  asphalts,  which  are  often  hard  to  distinguish  from 
some  of  the  natural  products.  For  use  as  road  binders,  the 
California  oils  are  undoubtedly  superior  to  all  others. 

In  1908,  the  California  field  produced  about  25  per  cent  of  the 
total  output  of  the  United  states,  and  sold  at  an  average  price 
of  fifty-two  cents  per  barrel,  which  is  lower  than  that  of  any  of 
the  other  oils,  except  those  of  the  Mid-Continent  field. 

The  "characteristics  of  a  typical  California  oil  residuum  are 
shown  below: 

(a)     CALIFORNIA    OIL    RESIDUUM. 

PHYSICAL  PROPERTIES. 

Specific  gravity,  2$°/2$0  C i  .006 

Flash,  degrees  C • 191° 

CHEMICAL  CHARACTERISTICS. 

Loss,  160°  C.,  7  hours 3.2% 

Character  of  residue Soft. 

Loss,  200°  C.,  7  hours  (fresh  sample) 17 . 3% 

Character  of  residue Soft. 

Bitumen  soluble  in  CS2,  air  temperature 99.  7% 

Organic  matter  insoluble o .  3% 

Inorganic  matter o .  o% 

100.  o 

Bitumen  insoluble  in  88°  naphtha,  air  temperature 7-7% 

Per  cent  of  soluble  bitumen  removed  by  H2SO4 54.9% 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons 41.9% 

Per  cent  of  solid  paraffin 0.0% 

Fixed  carbon 6 .  o% 

Other  Fields.  —  Oils  from  the  other  fields  have  not  been  as 
closely  studied  as  the  preceding,  but  a  few  observations  may  be 
made  as  to  their  characteristics.  In  general  the  Wyoming  oils 


PETROLEUM  AND  PETROLEUM  PRODUCTS       153 

vary  from  semiasphaltic  to  the  almost  wholly  asphaltic,  while 
the  Colorado  oils  seem  to  be  rich  in  paraffins  and  are  in  many 
respects  similar  to  the  eastern  petroleums.  To  the  author's 
knowledge,  neither  of  these  oils  has  been  employed  to  any 
extent  as  a  dust  preventive  or  road  binder.  Oils  from  other 
individual  fields  resemble  either  the  Pennsylvania,  Texas  or 
California  oils,  which  may  be  considered  as  representing  the 
three  main  types. 

Owing  to  the  extremely  complex  nature  of  petroleums  and  the 
fact  that  one  type  blends  into  another,  only  the  very  broadest 
distinction  can  be  made  between  the  different  types,  and  the 
preceding  description  of  characteristics  of  oils  from  the  various 
fields  should  be  considered  in  this  light,  as  no  one  oil  will  exactly 
duplicate  another  even  in  the  same  field. 

Occurrence  of  Petroleum.  —  Petroleum  is  not  limited  to  any 
particular  geological  horizon,  but  is  found  in  rocks  of  all  ages 
from  the  lower  Silurian  to  the  most  recent.  It  is  generally 
found  in  sandstones  or  conglomerates  overlaid  with  an  imper- 
vious shale  or  slate.  In  many  places  it  comes  to  the  surface  in 
small  quantities  but  is  generally  obtained  by  boring  tube  wells 
through  the  shale  into  the  sand  rock.  After  the  deposit  or  well 
has  been  struck,  the  pressure  is  sometimes  so  great  as  to  drive 
the  oil  to  the  surface  with  much  force.  Such  wells  are  called 
gushers,  but  seldom  flow  for  more  than  a  few  days  without 
pumping  becoming  necessary.  In  many  cases  the  well  is  tor- 
pedoed in  order  to  bring  the  oil  to  the  surface.  This  is  done  by 
exploding  a  shell,  containing  nitroglycerin,  which  has  been 
lowered  to  the  bottom  of  the  well,  the  resulting  pressure  being 
sufficient  to  force  the  oil  out  of  the  boring  for  some  time.  The 
wells  vary  in  depth  from  50  to  4000  feet  and  over,  and  the  oil 
is  now  generally  carried  from  these  wells  to  the  refineries  by 
pipe  lines  through  which  it  is  pumped  from  station  to  station. 
When  the  crude  oil  is  extremely  viscous,  recourse  is  had  to 
a  pipe  rifled  in  much  the  same  manner  as  a  gun  barrel. 
A  small  quantity  of  water  is  pumped  with  the  oil,  and  this, 
owing  to  the  centrifugal  motion  caused  by  the  rifling,  finds  its 


154  DUST   PREVENTIVES   AND    ROAD   BINDERS 

way  to  the  inner  surface  of  the  pipe  and  serves  as  a  lubricant 
between  it  and  the  oil. 

Crude  petroleum  is  an  oily  liquid  of  rather  unpleasant  odor 
with  a  specific  gravity  ranging  from  0.73  to  0.98  and  higher 
according  to  the  locality  from  which  it  is  derived.  It  varies  in 
color  from  greenish  brown  to  nearly  black  and  often  exhibits 
a  reddish  brown  or  orange  color  when  viewed  by  transmitted 
light.  It  is  also  somewhat  fluorescent.  Sand  and  water  are 
often  mixed  with  the  crude  oil  but  these  separate  and  settle 
upon  standing  in  the  storage  tanks.  Crude  petroleum  has  been 
used  to  some  extent,  especially  in  California,  for  direct  appli- 
cation as  a  dust  preventive.  It  has  also  been  employed  in  con- 
siderable quantities  as  a  fuel  and  in  some  instances  has  been 
used  as  a  lubricant  without  previous  treatment.  In  order  to 
recover  various  products  from  the  crude  petroleum  it  is  sub- 
jected to  a  process  of  refining  by  means  of  fractional  distilla- 
tion. In  general  the  process  is  carried  on  as  follows,  with  the 
production  of  five  fractions,  the  naphthas,  the  illuminating  oils, 
the  lubricating  oils,  paraffins  and  the  residue  which  if  distilla- 
tion is  carried  to  a  finish  becomes  coke.  The  higher  the  yield 
of  illuminating  oils  the  greater  the  value  of  the  crude  material. 
Many  crude  products  are,  however,  distilled  for  lubricating  oils 
only.  The  process  of  refining  is  for  the  most  part  worked  in 
two  stages,  the  light  oils  being  removed  in  the  first  and  the 
heavier  oils  in  the  second. 

Oil  Stills.  —  There  are  two  forms  of  stills  used  for  distilling 
the  light  oils,  the  cylindrical  and  the  cheese  box.  The  former  is 
most  commonly  employed  in  this  country.  It  is  constructed 
of  iron  and  is  set  in  a  horizontal  position  in  a  brick  furnace  with 
the  upper  half  exposed  to  the  air  as  shown  in  Fig.  14.  It  is 
fitted  with  steam  coils  for  quickly  heating  the  whole  mass  of 
oil,  and  sometimes  with  an  arrangement  for  blowing  in  free 
steam  which  assists  mechanically  in  carrying  over  the  oil  vapors 
through  the  dome  and  exit  pipe  to  the  condensers.  The  cheese 
box  still  is  set  directly  over  the  furnace  and  all  except  the  bottom 
is  exposed  to  the  outside  air.  It  is  also  fitted  with  steam  coils 


PETROLEUM  AND  PETROLEUM  PRODUCTS 


155 


and  jets  and  the  bottom  is  double  curved  to  admit  of  expansion. 
It  is  not  now  very  generally  employed.  The  condensers  consist 
either  of  coils  of  iron  pipe  or  batteries  of  parallel  pipes  cooled 


FIG.  14.     Oil  Still. 

with  water.  They  are  usually  provided  with  traps  by  means 
of  which  the  gases  passing  over  with  the  oils  are  collected  and 
led  under  the  still  to  be  burned. 

Preliminary  Refining.  —  In  carrying  on  this  operation,  the 
oil,  which  has  been  allowed  to  settle  in  the  storage  tank  until 
the  mud  and  water  have  settled  out,  is  charged  into  the  still 
and  heated  by  means  of  the  furnace  and  the  steam  coils  until 
the  first  fraction,  or  naphthas,  begins  to  flow  from  the  condenser. 


156  DUST   PREVENTIVES    AND    ROAD    BINDERS 

When  the  fractions  boiling  as  high  as  150°  C.  have  appeared, 
the  distillate  has  a  specific  gravity  of  about  .729  and  the  oils 
thus  collected  are  reserved  for  further  fractionation  and  puri- 
fication. The  oils  from  150°  to  300°  C.,  having  a  specific  grav- 
ity of  from  .790  to  .820,  next  appear  and  are  collected  for 
further  purification,  after  which  they  are  employed  for  illumi- 
nating purposes.  These  are  known  as  kerosenes  or  burning  oils, 
and  as  they  are  the  most  valuable  of  any  of  the  constituents,  a 
method  known  as  "cracking,"  which  increases  their  yield,  is 
very  generally  employed.  As  soon  as  the  heavy  oils  begin  to 
appear  the  fire  is  modified  so  that  only  the  bottom  of  the  still 
is  heated  very  hot,  while  the  top  and  sides,  being  exposed  to  the 
air,  become  somewhat  cooled.  The  heavy  oil  vapors  are  there- 
fore condensed  within  the  still  itself  and  upon  dropping  back 
into  the  residuum,  which  is  much  hotter  than  their  boiling 
points,  break  up  into  lighter  oils  with  lower  boiling  points  and 
often  with  a  separation  at  the  same  time  of  free  carbon  or  coke, 
which  is  deposited  upon  the  bottom  of  the  still. 

Further  Refining.  —  The  residuums,  or  reduced  oils,  pro- 
duced by  the  method  of  distillation  which  has  been  described, 
are  often  further  treated  to  remove  the  burning  oils  and  paraf- 
fins. For  this  purpose  they  are  transferred  to  a  cylindrical 
still  set  in  much  the  same  way  as  the  one  for  removing  the 
lighter  oils.  This  still  is  called  the  tar  still  and  is  usually 
smaller  than  the  one  previously  mentioned.  It  is  fitted  with 
pipes  for  introducing  superheated  steam.  The  distillate  up  to 
400°  C.  constitutes  the  lubricating  oils.  These  often  contain 
a  considerable  amount  of  paraffin  scale,  which  is  separated  by 
further  treatment.  The  oils  containing  solid  paraffins  are  the 
last  to  appear  and. if  distillation  is  carried  far  enough  the  residue 
becomes  coke.  If  distillation  is  not  carried  to  this  point  and 
the  petroleum  is  a  paraffin  one,  the  residue  remaining  after  the 
greater  part  of  the  oils  have  been  removed  is  treated  to  recover 
vaseline  as  well  as  paraffin.  Sometimes  distillation  is  carried 
on  in  vacuo,  by  which  means  the  heavier  distillates  are  removed 
at  a  lower  temperature  than  otherwise  and  cracking  is  avoided 


I 


PETROLEUM  AND  PETROLEUM  PRODUCTS       157 

to  a  considerable  extent.  This  is  desirable  if  a  large  yield  of 
solid  paraffins  is  to  be  obtained  or  an  artificial  asphalt  is  to  be 
produced. 

Some  residues  are  employed  as  fuel,  having  little  value  for 
any  other  purpose,  some  which  should  be  used  as  a  fuel  are  sold 
as  road  preparations  and  their  use  for  road  treatment  has  re- 
sulted in  many  failures.  If  distillation  is  carried  to  the  point 
where  a  solid  residuum  is  obtained  upon  cooling,  an  artificial 
asphalt  is  produced,  providing  the  crude  oil  is  asphaltic  in  char- 
acter. The  artificial  asphalts  have  been  extensively  employed 
in  recent  years  in  the  paving  industry  and  are  now  being  sold  to 
some  extent  as  road  binders. 

Cracking.  —  The  chemistry  of  the  cracking  process  is  ex- 
ceedingly complex  and  but  little  understood.  Under  the  varying 
conditions  at  which  it  takes  place,  including  pressure,  tempera- 
ture and  character  of  the  oil  distilled,  reactions  involving  any 
or  all  of  the  hydrocarbon  series  may  occur  accompanied  by 
the  splitting  up  and  polymerization  of  certain  compounds.  At 
such  times  the  gaseous  components  present  in  the  still  are  in 
an  extremely  unstable  state  of  equilibrium  and  are  ready  to 
break  up  or  react  with  one  another  in  different  ways  to  form 
varying  products,  according  to  slight  variations  in  tempera- 
ture and  pressure.  It  is  certain,  however,  that  the  general 
tendency  of  these  reactions  is  towards  the  formation  of  unsatu- 
rated  compounds  as  shown  by  the  behavior  of  the  distillates 
with  sulphuric  acid.  Thus  the  hydrocarbon  C20H42  might  be 
resolved  into  C5H12  +  C15H30,  or  C6H14  +  C14H28,  etc.,  the  gen- 
eral equation  of  the  decomposition  being: 

CnH2n+2+  heat  =  C(n_p)H2(n_p)+2  +  CpH2p 

paraffin  paraffin  Olefine 

According  to  Thorpe  and  Young  *  the  product  actually  ob- 
tained is  a  mixture  of  several  paraffins  and  several  olefines. 

If  the  cracking  process  is  not  carried  too  far,  certain  hydro- 
carbons of  asphaltic  characteristics  may  be  formed,  but  if  it  is 

*  Ber.  des  Deutsch.  Chem.  Gesellsch.,  1872,  p.  536. 


158  DUST   PREVENTIVES   AND    ROAD   BINDERS 

carried  beyond  this  point  inert  coke  or  free  carbon  is  deposited 
in  the  residuum.  The  presence  of  this  substance  in  any  quan- 
tity is  direct  evidence  that  the  oil  has  been  cracked.  There  is 
a  much  greater  tendency  for  asphaltic  oils  to  crack  at  compara- 
tively low  temperatures  than  the  paraffin  oils  and  for  this 
reason  where  it  is  desired  to  produce  a  residuum  suitable  for 
road  or  paving  work,  great  care  should  be  taken  in  distilling  for, 
even  if  the  stills  are  subjected  to  a  uniform  temperature,  crack- 
ing begins  to  take  place  at  ordinary  pressures  before  residuums 
of  sufficient  consistency  can  be  secured,  and  for  this  reason  the 
vacuum  process  with  or  without  the  use  of  superheated  steam 
is  largely  employed.  By  this  means  residues  are  produced 
which  more  nearly  resemble  the  semisolid  and  solid  native 
bitumens  than  if  the  distillation  were  conducted  under  normal 
conditions.  It  should  be  remembered,  however,  that  the  native 
bitumens  have  been  formed  under  conditions  which  it  has  so 
far  been  impossible  to  reproduce  either  in  the  laboratory  or 
factory,  and  the  exact  duplication  of  native  products  has,  there- 
fore, been  an  impossibility.  While  the  asphaltic  oils  if  care- 
fully distilled  or  evaporated  may  be  converted  into  artificial 
asphalts,  closely  resembling  the  native,  this  can  be  only  par- 
tially accomplished  with  the  semiasphaltic  oils  and  not  at  all 
with  paraffin  petroleums.  For  this  reason  the  California  oils 
are  far  superior  to  those  from  other  fields,  for  the  purpose  of 
manufacturing  artificial  asphalts.  In  general  it  may  be  said 
that  as  asphalts  are  produced  from  certain  oils  in  nature  by 
evaporation,  decomposition  and  polymerization  of  certain  classes 
of  hydrocarbons  so  also  are  the  artificial  asphalts  by  similar 
artificial  processes,  but  the  temperatures  required  to  bring  about 
these  results  in  the  latter  case  are  probably  greater  than  in  the 
former,  owing  to  the  necessarily  rapid  conversion  and  lower 
pressure. 

Blown  Oils  and  Similar  Products. —  In  nature  oxidation  or 
dehydrogenezation  undoubtedly  plays  an  important  part  in  the 
formation  of  asphalts  and  this  is  caused  by  the  action  of  some 
strong  oxidizing  agent  such  as  oxygen  or  sulphur.  These  sub- 


PETROLEUM  AND  PETROLEUM  PRODUCTS       159 

stances  may  react  with  two  similar  hydrocarbon  molecules  to 
form  a  single  hydrocarbon  together  with  water  or  hydrogen 
sulphide  gas  (H2S).  When  such  reactions  occur  between  ring 
compounds  a  nucleus  condensation  often  results.  The  formation 
of  the  poly  cyclic  polymethylenes  is  thus  explained.  This  method 
of  nucleus  condensation  may  be  represented  by  the  following 
general  reactions: 

(1)  aCnH2n  +  &S  =  CanH2an_26       +  &H2S 

Polyraethylene  +  Sulphur  =  Polycyclic   Polymethylene  +  Hydrogen  Sulphide. 

(2)  aCnH2re     +    &O  CanH2ari_2&          +  &H2O 

Polymethylene  +  Oxygen.          =  Polycyclic  Polymethylene  +  Water. 

Other  reactions  in  which  the  elements  actually  combine  with 
the  hydrocarbons  to  form  sulphuretted  or  oxygenated  com- 
pounds may  also  occur.  Attempts  have  been  made  to  repro- 
duce these  reactions  in  the  still  by  artificial  means.  The  first 
artificial  asphalt  made  in  this  manner  was  produced  by  the 
action  of  sulphur,  which  was  added  to  an  ordinary  paraffin 
petroleum  residuum  while  hot  after  the  distillation  had  been 
stopped.  Hydrogen  sulphide  gas  was  evolved  and  the  residuum 
was  thickened  considerably,  but  became  very  cheesy.  This 
method  was  known  as  the  Dubbs  process  and  was  succeeded  by 
that  of  Byerly,  who  found  that  much  the  same  results  could 
be  produced  by  blowing  a  jet  of  air  through  the  hot  residue  in 
practically  the  same  way  that  certain  vegetable  oils  are  treated 
in  order  to  thicken  them.  Products  of  this  nature  are  now 
manufactured  to  a  large  extent,  and  are  generally  known  as 
blown  oils.  The  paraffin  hydrocarbons  are  little  acted  upon 
by  oxygen,  even  at  comparatively  high  temperature,  so  that  the 
thickening  of  paraffin  petroleums  by  this  means  is  largely 
dependent  upon  the  reactions  taking  place  between  the  oxygen 
and  hydrocarbons  of  other  series.  Unless  considerable  quan- 
tities of  asphaltic  hydrocarbons  are  present,  in  which  case  the 
oil  would  be  semiasphaltic,  blown  oils  are  of  no  value  as  road 
binders.  The  semiasphaltic  blown  oils  are  now  used  to  a  con- 
siderable extent  in  the  treatment  of  roads  and  promise  to  be  of 


160  DUST   PREVENTIVES    AND    ROAD   BINDERS 

value  if  the  blowing  process  has  not  been  carried  too  far  and  if 
only  a  comparatively  small  percentage  of  heavy  paraffin  hydro- 
carbons is  present.  They  exhibit  fairly  good  binding  qualities 
and  have  the  advantage  of  being  less  susceptible  to  tempera- 
ture changes  than  almost  any  other  type  of  bitumen.  Their 
main  drawback  seems  to  lie  in  the  fact  that  they  are  not  ductile, 
but  in  the  case  of  soft  and  medium  hard  products  this  is  not 
an  exceedingly  serious  objection.  They  have  a  tendency  to 
harden  with  age,  but  so  also  have  the  truly  asphaltic  oils  and 
this  should  be  remembered  when  selecting  a  road  binder,  in 
order  that  too  brittle  a  product  may  not  be  formed  under 
service  conditions.  An  analysis  of  a  typical  blown  oil  sold  as  a 
road  binder  is  given  below  for  the  sake  of  comparison  with  other 
oil  residuums. 

SEMIASPHALTIC    BLOWN    OIL    RESIDUUM. 

Specific  gravity,  2$0/2$0  C 974 

Flash,  degrees  C 260° 

Melting  point,  degrees  C 55° 

Penetration,  25°  C.,  No.  2  N.,  100  gms.,  5  sec . 136° 

Loss  at  163°  C.,  7  hours o.  18% 

Loss  at  205°  C.,  7  hours o .  68% 

Character  of  residue  (dense,  sticky,  somewhat  harder  than  origi- 
nal material) . 

Soluble  in  CS2,  air  temperature 99.92% 

Bitumen  insoluble  in  72°  naphtha,  air  temperature 16.36% 

Bitumen  insoluble  in  86°  naphtha,  air  temperature 22 .05% 

Per  cent  of  soluble  bitumens  removed  by  H2SO4 25. 16% 

Per  cent  of  soluble  bitumens  as  saturated  hydrocarbons 74.84% 

Bitumen  insoluble  in  CC14,  air  temperature 0.00%' 

Paraffin  scale  (strongly  colored) 5-i% 

Acid  Sludge.  —  In  the  purification  of  certain  distillates 
obtained  from  crude  petroleums,  sulphuric  acid  is  often  used 
to  remove  the  unsaturated  compounds.  Sulphones  and  other 
complex  compounds  are  formed  and  separated  from  the  satu- 
rated hydrocarbon  oils  by  subsidence.  This  material  is  known 
as  acid  sludge  and  often  solidifies  upon  standing.  It  is  usually 
considered  a  waste  product,  but  is  sometimes  sold  as  a  road 
binder.  Such  material,  while  possessing  fair  adhesive  qualities, 


PETROLEUM  AND  PETROLEUM  PRODUCTS      l6l 

is  unsuited  for  use  as  a  permanent  binder  owing  to  the  fact  that 
it  is  quite  readily  acted  upon  by  water,  being  partially  soluble 
and  easily  disintegrated. 

Crude  Oils.  —  While  refined  oils  or  oil  residuums  are  usually 
of  much  greater  value  than  crude  oils  for  road  treatment,  the 
latter  have  been  employed  to  some  extent  for  this  purpose, 
especially  in  California.  The  different  characteristics  of  oils 
from  the  various  fields  have  already  been  shown  by  analyses  of 
their  residuums  and  these  residuums  will  be  further  discussed 
with  reference  to  their  suitability  for  road  purposes.  Before 
doing  this,  however,  it  may  be  well  to  briefly  consider  the  crude 
petroleums.  In  general  it  may  be  said  that  the  value  of  an 
oil  for  road  purposes  is  directly  proportional  to  the  amount 
of  true  binding  base  which  it  holds  or  is  capable  of  producing 
after  application.  Paraffin  oils  are  wholly  lacking  in  both 
respects  and  are,  therefore,  unsuited  for  road  treatment.  They 
may  be  employed  solely  as  dust  preventives,  but  being  of  an 
inherently  greasy  nature,  they  hold  the  dust  down  by  force  of 
capillarity  only.  If  applied  in  any  considerable  quantity  they 
form  a  slippery  oily  mud  in  wet  weather,  which  is  ruinous  to 
clothes  and  the  paint  on  vehicles,  besides  being  extremely  dis- 
agreeable to  persons  driving  over  the  roads.  Crude  semi- 
asphaltic  oils  are  less  objectionable,  but  can  only  be  considered 
as  temporary  or  at  best  as  semipermanent  binders.  They 
possess  the  same  chemically  stable  characteristics  as  the  paraffin 
oils  and  after  application  are  capable  of  developing  a  higher 
binding  value  only  by  volatilization  of  the  lighter  constituents 
under  atmospheric  conditions.  A  natural  residuum  may  thus 
be  produced  in  situ  but  it  will  always  be  more  oily  than  sticky 
on  account  of  the  presence  of  a  large  amount  of  non-volatile 
fluid  paraffin  constituents.  The  truly  asphaltic  crude  oils,  on 
the  other  hand,  are  inherently  adhesive  and  after  application 
are  capable  of  being  gradually  transformed  under  atmospheric 
conditions  into  almost  true  asphalts.  This  transformation  is 
not  entirely  dependent  upon  evaporation,  for  the  sulphur  which 
is  always  present  and  probably  atmospheric  oxygen  react  to 


162 


DUST  PREVENTIVES   AND   ROAD   BINDERS 


form  nucleus  condensation  products  in  approximately  the  same 
way  that  many  native  asphalts  are  formed.  A  gradual  harden- 
ing of  the  road  surface,  therefore,  takes  place  and  the  mineral 
aggregate  becomes  more  firmly  bonded  and  consolidated. 

It  is  not  a  difficult  matter  to  distinguish  between  the  crude 
asphaltic  and  paraffin  petroleums,  for  the  former  are  usually 
darker  in  color  and  much  more  viscous  and  sticky  than  the 
latter.  This  adhesiveness  is  particularly  noticeable  if  a  small 
quantity  of  the  oil  is  rubbed  between  the  thumb  and  forefinger 
until  the  greasy  constituents  are  absorbed  by  the  skin.  When 
so  tested,  paraffin  oils  are  completely  absorbed,  while  the  ad- 
hesiveness of  the  asphaltic  oils  becomes  more  pronounced. 

The  following  table  of  analyses  of  crude  oils,  embracing  the 
three  types,  paraffin,  semiasphaltic,  and  asphaltic,  serves  to  show 
some  of  their  differences  in  properties.  These  results  do  not  in 
any  sense  represent  absolute  values  for  the  different  classes, 
but  will  serve  to  give  a  general  idea  of  the  relative  character- 
istics of  each. 

CRUDE    PETROLEUMS. 


Pennsylvania 
Paraffin. 

Texas  Semi- 
asphaltic. 

California 
Asphaltic. 

Specific  gravity,  25°/25°  C 

80  1 

OTA 

Flash,  degrees  C  

Ord   temp 

43° 

26° 

Volatility  at  uo°C,  7  hours  

47-3% 

20% 

Volatility  at  160°  C,  7  hours  

S8.o% 

27% 

Volatility  at  205°  C,  7  hours  
Residue  

68.0% 

12    0% 

49% 
Si% 

42-7% 

*C7     7% 

Character  of  residue  

Soft 

Quick  flow 

0  /  •  6  /O 

Soft  maltha 
sticky 

*  Volatility  at  200°,  7  hours. 

It  will  be  noticed  from  the  foregoing  results  that  in  the 
samples  examined  the  specific  gravity  increases  from  the  paraf- 
fin to  the  asphaltic  oil.  This  is  also  true  of  the  percentage  of 
residue,  while  the  volatility  decreases  correspondingly.  The 
residues  vary  in  character  from  soft  and  greasy  through  an 
intermediate  and  but  slightly  viscous  nature  to  the  more  or 


PETROLEUM  AND  PETROLEUM  PRODUCTS      163 

less  liquid  maltha  of  good  adhesive  properties.  A  rough  idea  of 
the  character  of  these  bases  may  be  formed,  as  in  the  case  of 
the  crude  oil,  by  rubbing  a  little  of  the  residue  between  the 
finger  and  thumb.  The  color  and  odor  will  also  indicate  the 
character  of  the  crude  material  to  those  familiar  with  the  dif- 
ferent varieties.  In  comparing  the  Pennsylvania  with  the 
Texas  oil  it  will  be  seen  that  the  former  carries  a  higher  per 
cent  of  light  oils  than  the  latter. 

The  characteristics  of  a  crude  oil  which  might  almost  be 
classed  as  a  permanent  binder  are  shown  in  the  following  analy- 
sis of  a  California  road  oil. 

CALIFORNIA    ROAD    OIL. 

Character black,  viscous,  sticky 

Specific  gravity,  25°/25°  C 0.984 

Flash,  degrees  C 160° 

Loss  at  100°  C.,  7  hours 5.2  5% 

Character  of  residue considerably  more  viscous  than  original 

Loss  at  163°  C.,  7  hours 16.4% 

Character  of  residue sticky,  very  viscous 

Loss  at  205°  C.,  7  hours 30 .  o% 

Character  of  residue solid  but  not  brittle 

Soluble  in  CS2,  air  temperature 99-77% 

Organic  matter  insoluble .  12% 

Inorganic  matter .11% 


Bitumen  insoluble  in  86°  naphtha,  air  temperature 9-8% 

Fixed  carbon 2 . 05% 

Note.  —  This  oil  contained  a  small  amount  of  water. 

It  will  be  seen  from  the  volatility  tests  that  this  oil  is  capable 
of  increasing  greatly  in  consistency  after  application  and  would 
serve  as  an  excellent  binding  medium. 

Oil  Distillates.  —  Oil  distillates  are  but  little  used  in  the 
treatment  of  roads,  except  as  fluxes  for  the  heavier  residual 
products.  If  employed  in  their  natural  state,  they  are  of  value 
as  dust  preventives  only  and  should  be  applied  sparingly,  for 
they  contain  no  true  binding  base  and  are  inherently  oily. 
They  can  only  be  considered  as  poor  material  at  best  in  this 


1 64  DUST  PREVENTIVES   AND   ROAD   BINDERS 

connection.     These  distillates  are  heavy  in  nature  and  have 
usually  been  treated  for  the  extraction  of  solid  paraffine. 

The  results  of  an  examination  of  such  an  oil  distillate  are 
given  below: 

HEAVY    OIL    DISTILLATE. 

Specific  gravity,  2$°/2$°  C 0.894 

Flash,  degrees  C 100° 

Burning  point,  degrees  C 155° 

Viscosity  at  25°  C.,  degrees  Engler 3-3° 

Loss  at  163°  C.,  7  hours 12 . 88% 

Loss  at  205°  C.,  7  hours 25 . 60% 

Character  of  residue Oily,  fluid 

Paraffin  scale o .  62% 

If  such  a  distillate  is  heated  at  high  temperatures  in  an  open 
dish  for  a  considerable  length  of  time,  a  certain  amount  of 
solid  residue  will  be  produced.  This  residue,  however,  is  not 
present  in  the  original  oil  but  is  formed  at  the  high  tempera- 
tures by  decomposition  and  cracking  of  some  of  the  hydrocar- 
bons present.  When  it  is  desired  to  ascertain  the  character  of 
the  base  held  by  an  oil,  205°  C.  should  under  ordinary  condi- 
tions be  the  highest  temperature  employed.  This  material 
should,  therefore,  be  considered  as  holding  no  true  binding 
base. 

Oil  distillates  have  been  employed  in  the  manufacture  of  cut- 
back products,  but  for  this  purpose  should  be  quite  volatile,  in 
order  that  they  may  evaporate  after  application.  Cut-back 
products  are  solid  oil  residues  fluxed  with  distillates  to  any 
desired  consistency.  The  distillate  should  serve  merely  as  a 
carrying  agent  for  the  true  binding  residue  and  thus  facilitate 
application,  after  which  it  should  volatilize  and  leave  the  original 
residue  in  place.  Such  distillates  as  shown  above  are  unsuited 
for  this  purpose  because  they  are  not  sufficiently  volatile,  and 
any  mixture  in  which  they  may  be  employed  will  maintain  its 
original  consistency  indefinitely  after  application.  Fluxes  of 
this  nature  should  be  employed  only  to  bring  a  hard  bitumen 
to  the  consistency  which  it  is  desired  to  maintain  on  the  road 


PETROLEUM   AND  PETROLEUM  PRODUCTS  165 

and  for  this  purpose  a  fluid  oil  residuum  is  as  a  rule  to  be 
preferred. 

Cut-Back  Oils.  —  If  a  fluid  cut-back  product  is  to  be  used 
successfully  as  a  binder  in  road  construction,  the  distillate  flux 
should  be  volatile  at  as  low  a  temperature  as  possible.  When 
heated  in  an  open  dish  for  five  hours  at  a  maximum  tempera- 
ture of  163°  C.,  the  preparation  should  produce  a  residue  of 
the  desired  consistency  and  if  it  does  not,  there  is  little  chance 
of  the  oil  proving  satisfactory  under  service  conditions.  Con- 
sistency of  the  residuum  is  of  course  not  the  only  thing  to  be 
considered,  but  it  is  one  of  the  most  important  to  be  noted  after 
the  chemical  characteristics  of  the  oil  itself  have  been  ascer- 
tained. Methods  for  determining  these  characteristics  will  be 
described  in  a  later  chapter. 

The  results  of  an  examination  of  an  excellent  cut-back  oil  for 
road  work  are  given  below: 

CUT-BACK   ROAD    OIL. 

Character Viscous,  sticky,  fluid 

Specific  gravity,  2$°/2$°  C o .  942 

Flash,  degrees  C 32° 

Burning  point,  degrees  C 34° 

Loss  at  100°  C.,  5  hours 18. 63% 

Loss  at  163°  C.,  5  hours 20. 12% 

Character  of  residue dense,  semiasphaltic 

Penetration  of  residue,  25°  C.,  No.  2  N,  100  g.,  5  sec 106 

Bitumen  soluble  in  CS2,  air  temperature 99.90% 

Organic  matter  insoluble .  08% 

Inorganic  matter 02% 

100.00 

Bitumen  insoluble  in  86°  naphtha 17.0  % 

Fixed  carbon 6. 64% 

From  this  examination  it  is  evident  that  the  product  is  a 
dense  artificial  asphalt  which  has  been  fluxed  with  about  one- 
fourth  its  weight  of  a  light  volatile  flux.  The  former  fact  is 
indicated  by  the  character  and  penetration  of  the  residue  ob- 
tained from  heating  the  oil  at  163°  C.  and  the  latter  by  the  loss 
at  1 00°  C.,  the  low  flash  and  rather  low  specific  gravity.  In 
some  respects  a  higher  flash  point  would  be  more  desirable.  That 


1 66  DUST  PREVENTIVES   AND   ROAD   BINDERS 

this  material  will  quickly  come  to  and  be  maintained  at  its 
maximum  consistency  is  shown  by  the  close  agreement  of  the 
loss  at  1 00°  and  163°  C.  The  high  solubility  in  carbon  bisul- 
phide shows  it  to-  be  an  exceedingly  pure  bitumen  and  the 
high  percentage  of  bitumen  insoluble  in  86°  Baume  naphtha 
indicates  very  good  asphaltic  properties  which  have  not  been 
produced  entirely  by  blowing,  as  shown  by  the  medium  amount 
of  fixed  carbon.  The  penetration  of  the  residue  indicates  that 
the  true  binding  base  is  of  suitable  consistency  for  road  con- 
struction, and  the  high  volatility  and  low  flash  that  the  original 
material  must  be  applied  without  heating. 

Fluid  Oil  Residuums.  —  The  residuums  of  the  various  petro- 
leums have  been  used  to  a  great  extent  both  as  fluxes  for  the 
solid  native  bitumens  and  as  substitutes  for  the  same  in  the 
paving  industry.  Their  various  characteristics  and  properties 
have  therefore  been  given  considerable  attention,  and  from  the 
standpoint  of  road  treatment,  the  results  obtained  from  a  study  of 
these  fluxes  and  artificial  asphalts  should  be  of  service  in  deter- 
mining the  suitability  of  various  oils  for  this  purpose.  The 
characteristics  of  the  residues  will  naturally  vary  as  the  crude 
petroleums  vary,  although  as  has  been  shown  they  may  be  con- 
siderably influenced  by  the  method  of  preparation. 

The  paraffin  petroleum  residuums  are  of  a  soft  greasy 
character  and,  as  their  name  implies,  contain  a  large  amount  of 
paraffin  hydrocarbons  and  paraffin  scale  or  crude  paraffin. 
A  road  surface  treated  with  material  of  this  nature  will  be 
dustless  for  the  time  being  but  in  damp,  rainy  weather  will 
become  covered  with  a  slimy,  greasy  mud  which  is  easily  washed 
away,  leaving  the  road  in  as  bad  condition  as  it  was  before 
treatment,  if  not  worse.  Even  when  used  solely  as  a  flux  for 
asphalt  the  paraffin  scale  is  apt  to  cause  bad  results  if  present 
to  the  extent  of  over  10  per  cent.  When  the  crude  or  even  the 
residual  oil  is  used  as  a  binder,  it  is,  therefore,  only  to  be  supposed 
that  the  outcome  will  prove  a  failure.  The  base  held  by  Cali- 
fornia petroleums  is  composed  of  bitumens  resembling  asphalt. 
The  residuum  as  a  rule  contains  no  paraffin  and  if  cracking  has 


PETROLEUM  AND  PETROLEUM  PRODUCTS 


I67 


not  been  employed  in  its  preparation  shows  but  little  free  car- 
bon. As  has  been  stated  they  are  the  most  satisfactory  type 
for  use  as  dust  preventives  and  road  binders. 

While  the  properties  of  the  residuums  produced  by  petro- 
leums from  the  various  fields  have  already  been  given,  the 
differences  can  better  be  seen  by  a  direct  comparison.  Three 
typical  fluid  oil  residues  are,  therefore,  shown  in  the  following 
table: 

FLUID    PETROLEUM  RESIDUES. 


Pennsylvania 
Paraffin. 

Texas  Semi- 
asphaltic. 

California 
Asphaltic. 

Specific  gravity,  25°/25°  C  

O.Q2O 

O  074 

I   006 

Flash,  degrees  C        

186° 

214° 

101° 

Loss  at  1  60°,  7  hours  

?.*% 

0.8% 

S-2% 

Character  of  residue  

Soft 

Soft 

Soft 

Loss  at  20  ^°   7  hours 

14    2% 

6    2% 

17    3% 

Character  of  residue 

Soft 

Soft 

Soft 

Bitumen  soluble  in  CS2 

OQ  8% 

QO  6% 

on    7% 

Organic  matter  insoluble    .... 

0.2% 

o  4% 

0    3% 

Inorganic  matter  

0.0% 

0.0% 

O    0% 

Bitumen  insoluble  in  88°  naphtha  .... 
Per  cent  of  soluble  bitumen  removed 
by  H,SO4 

100.  0 

4.3% 

21  .0% 

100.  0 

4-8% 

20    Q% 

IOO.O 

7-7% 

CA     Q% 

Per  cent  of  total  bitumen  as  saturated 
hydrocarbons  

74.8% 

70.4% 

41    0% 

Paraffin  scale 

II    O 

I    7% 

O    O°7n 

Fixed  carbon 

3    O 

1    S% 

6  o% 

In  comparing  these  results  an  increase  in  specific  gravities 
running  in  the  same  direction  as  those  for  the  crude  petroleums 
will  be  noticed.  The  flash  point  and  volatility,  however,  are 
not  graded.  As  they  are  of  course  due  entirely  to  the  point 
at  which  distillation  is  stopped,  in  the  process  of  refining,  this 
is  only  to  be  expected.  As  shown  by  the  test  for  solubility  in 
carbon  bisulphide,  these  oils  are  practically  pure  bitumens. 
The  material  insoluble  in  88°  naphtha  is  found  to  increase  from 
the  Pennsylvania  to  the  California  oil,  which  indicates  an 
increase  in  body  of  the  oils.  It  will  be  noticed  that  a  much 


1 68  DUST  PREVENTIVES  AND   ROAD   BINDERS 

higher  percentage  of  unsaturated  hydrocarbons  is  present  in 
the  California  oil  than  in  the  other  two.  The  percentage  of 
solid  paraffins  on  the  other  hand  decreases  from  the  Pennsyl- 
vania to  the  California  oil.  The  latter  rarely  contains  any 
paraffin  scale,  while  the  former  often  holds  as  high  as  30  per 
cent  and  over.  The  percentage  of  fixed  carbon  runs  in  the 
opposite  direction  and  this,  like  the  percentage  of  naphtha 
insoluble  bitumen,  indicates  the  relative  amount  of  body  form- 
ing hydrocarbons  which  tend  to  produce  mechanical  stability. 

In  comparing  the  crude  oils  with  the  residuums,  it  will  be 
seen  that,  for  the  same  type,  the  specific  gravity  and  flash  point 
of  the  former  are  lower  and  that  the  volatility  is  higher,  as 
would  naturally  be  expected.  Other  things  being  equal,  there- 
fore, the  residual  oils  should  be  preferable  for  road  treatment, 
because  of  the  concentration  of  any  binding  base  which  may  be 
present.  In  all  cases,  however,  the  use  of  truly  paraffin  oils 
should  be  avoided  and  those  which  more  nearly  approach  the 
California  type  be  given  preference. 

Owing  to  the  method  now  commonly  employed  of  piping 
crude  oil  from  wells  to  the  storage  tanks,  making  use  of  the 
same  line  to  carry  oils  from  a  great  number  and  variety  of 
wells,  it  is  often  a  difficult  matter  to  obtain  two  lots  of  oil 
showing  the  same  properties,  even  when  purchased  from  the 
same  source.  Added  to  this,  the  fact  that  at  the  present  time 
the  manufacturer  is  turning  out  a  great  variety  of  carelessly 
prepared  road  oils  makes  it  very  important  that  an  examination 
of  each  lot  be  made  before  attempting  to  use  it  for  road  pur- 
poses. Many  instances  might  be  cited  of  road  oils  varying 
inexcusably  in  character,  which  have  been  sold  under  the  same 
trade  name  as  representing  a  definite  product.  Until  certain 
standards  are  adhered  to,  it  is,  therefore,  useless  to  give  analyses 
of  trade  products  as  representing  anything  definite.  The 
properties  of  certain  fluid  residual  road  oils  as  now  found  upon 
the  market  are,  however,  given  in  the  table  below  in  order  to 
discuss  their  relative  value  as  dust  preventives  and  road 
binders. 


PETROLEUM  AND  PETROLEUM  PRODUCTS 


169 


FLUID    RESIDUAL    ROAD    OILS. 


No         

i 

2 

3 

Character        

Thin,  greasy 

Quite  viscous, 

Very  viscous, 

Specific  gravity,  25°/25°  C  

0.916 

Fairly  sticky 
0.960 

Sticky 
0.080 

Flash    degrees  C 

i^° 

243° 

Penetration,  25°  C.,No.  2  N,  100  g.  5  sec. 
Loss  at  163°  C  ,  5  hours            

_     *aO 

Too  soft 
8.86 

Too  soft 
0.49 

196° 

0.04% 

Character  of  residue  

Fluid,  granu- 

But little 

Sticky,  some- 

Penetration of  residue  (as  above)  
Soluble  in  CS2,  air  temperature  
Organic  matter  insoluble 

lar,  greasy 
Too  soft 
99-75 

,2< 

changed 
Too  soft 

100.0% 
0    0% 

what  harder 
142 

99-77% 

Oc;% 

Inorganic  matter  ...                    

o.oo 

0.0% 

0.18% 

Per  cent  bitumen  insoluble  in  86° 
naphtha,  air  temperature  

IOO.O 

2.28 

100.00 

5.12% 

100.00 
20.02% 

Fixed  carbon 

426 

47? 

II     ^3 

From  the  above  results  it  will  be  seen  that  oil  No.  i  is  a 
very  fluid  reduced  or  residual  oil,  as  shown  by  its  specific  gravity, 
flash  point  and  volatility.  While  probably  semiasphaltic 
in  character,  it  is  rich  in  paraffin  hydrocarbons,  which  fact  is 
indicated  by  the  granular  appearance  of  the  residue.  Its 
naphtha  insoluble  bitumen  and  fixed  carbon  are  low,  indicating 
poor  mechanical  stability,  and  while  its  loss  at  163°  C.  is  fairly 
high,  the  fact  that  the  residue  is  still  fluid  and  greasy  shows  it 
to  be  incapable  of  developing  good  binding  qualities  under 
service  conditions.  As  shown  by  its  solubility  in  carbon  bisul- 
phide, this  material  is  almost  pure  bitumen  and  the  same  is 
true  of  the  other  samples. 

Sample  No.  2  is  a  denser  residuum  whose  flash  point  indi- 
cates that  it  has  been  distilled  at  a  higher  temperature  than 
No.  i.  This  is  also  shown  by  the  volatility  test,  the  loss  at 
163°  C.  for  five  hours  being  less  than  half  of  i  per  cent.  As 
in  the  case  of  No.  i,  its  low  naphtha  insoluble  bitumen  and  low 
fixed  carbon  show  it  to  be  deficient  in  mechanical  stability  and 
the  character  of  its  residue,  from  the  volatility  test,  incapable  of 


I/O  DUST  PREVENTIVES   AND   ROAD  BINDERS 

improving  in  this  respect  under  service  conditions.  It  is, 
however,  somewhat  sticky  and  capable  of  serving  as  a  weak 
binder. 

Sample  No.  3  is  a  dense,  viscous  oil  residuum  almost  semi- 
solid  in  character  as  shown  by  the  penetration  test.  Its  very 
low  loss  when  heated  at  163°  C.  for  five  hours  proves  that  it 
has  been  distilled  at  a  higher  temperature  than  either  of  the 
other  two.  Its  sticky  character  indicates  good  binding  quali- 
ties and  its  rather  high  naphtha  insoluble  bitumen  and  fixed 
carbon  show  a  greater  degree  of  mechanical  stability,  which  is 
capable  of  being  further  developed  under  service  conditions  to 
some  extent,  this  being  indicated  by  the  decrease  in  penetration 
of  the  residue  from  the  volatilization  test  over  the  original 
material.  Its  high  naphtha  insoluble  contents  would  tend  to 
show  that  it  is  a  partially  blown  oil. 

From  the  foregoing  it  is  evident  that  an  increasing  value  for 
road  binding  exists  from  sample  No.  i  to  No.  3.  The  former 
can  only  be  considered  as  a  dust  preventive  at  best,  which 
has  practically  no  value  as  a  binder  and  is  suitable  only  for 
surface  application  in  small  quantities.  Owing,  to  its  fluid 
character  it  may  be  applied  cold  by  means  of  a  sprinkler. 
Sample  No.  2  may  be  classed  as  a  semipermanent  binder  suit- 
able for  surface  application  only  and  of  little  or  no  value  for  road 
construction.  It  should  preferably  be  applied  hot.  Sample  No.  3 
may,  on  the  other  hand,  be  considered  as  a  fairly  good  permanent 
binder,  suitable  for  construction  work  where  the  mineral  aggre- 
gate contains  a  sufficiently  large  quantity  of  coarse  particles  to 
produce  a  condition  of  stability  independent  of  that  of  the 
binder.  It  should  of  course  be  heated  before  applying,  and 
might  then  be  satisfactorily  employed  according  to  the  pene- 
tration method  which  will  be  described  in  a  later  chapter. 

Semisolid  and  Solid  Oil  Residuums.  —  Blown  oils  and  oil 
pitches  or  artificial  asphalts  constitute  the  semisolid  and  solid 
oil  residuums.  Most  of  those  now  on  the  market  are  semi- 
asphaltic  in  character  and  some  few  have  been  reinforced  by 
the  addition  of  a  small  amount  of  a  solid  native  bitumen  such 


PETROLEUM  AND  PETROLEUM  PRODUCTS 


I/I 


as  gilsonite,  for  the  purpose  of  increasing  their  body  and  bind- 
ing value.  They  are  employed  largely  as  fillers  for  brick  and 
block  pavements,  as  roofing  pitches,  for  sheet  asphalt  construc- 
tion and  also  in  the  construction  of  bituminous  macadam 
roads. 

According  to  a  recent  report*  of  the  Geological  Survey,  the 
production  of  oil  asphalts  in  the  United  States  for  1908  was 
102,281  short  tons,  valued  at  $1,322,616.  In  these  statistics, 
apparently  no  attempt  was  made  to  distinguish  between  the 
blown  oils  and  residual  pitches,  and  the  states  of  Cailfornia  and 
Texas  only  were  reported.  The  production  of  these  states  was 
as  follows: 


PRODUCTION    OF    OIL    ASPHALT    IN    1908. 


Quantity. 
(Short  tons.) 

Value. 

California          

8c,ii4 

$    072,176 

Texas  

17,167 

2  co,  440 

Total 

IO2  28l 

$i  322  616 

Had  the  blown  oil  products  of  the  mid-continent  and  southern 
Illinois  fields  been  included,  the  totals  would  have  been  very 
materially  increased,  as  the  output  from  the  former  in  particular 
is  quite  large. 

When  employed  in  road  construction  these  materials  should 
serve  as  permanent  binders  and  add  to  the  stability  of  the  road. 
It  is  necessary  to  heat  them  before  use  and  they  should  prefer- 
ably be  mixed  with  the  roadstone  before  it  is  laid.  They  act 
as  dust  preventives  only  by  reducing  road  disintegration  and 
wear  and  do  not  act  as  dust  layers.  Examples  of  this  class  of 
products  are  given  below.  They  are  usually  sold  under  the 
name  of  road  asphalts. 


*  "  Mineral  Resources  of  the  United  States,  Calendar  Year  1908." 


1/2  DUST  PREVENTIVES  AND   ROAD   BINDERS 

SOLID    OIL    RESIDUUMS. 


Character                

Semiasphaltic 

Semiasphaltic 
Residual 

Asphaltic 
Residual 

Blown  Oil. 

Pitch.* 

Pitch.* 

Color 

Dark  brown 

Black  lus- 

Black lus- 

Fracture                           

Cheesv 

trous 
Conchoidal 

trous 
Conchoidal 

Specific  gravity,  25°/25°  C  
Penetration,  25°  C.,  No.  2  needle,  100 
cms     <c  sec 

Q-995 

103° 

1.070 

7° 

1.071 

c;2° 

Loss    163°  C     7  hours 

0    00% 

QC% 

2    7% 

Penetration  of  residue  (as  above)  .    ... 

136° 

20° 

Bitumen  soluble  in  CS2,   air  temper- 
ature                  

QQ-  7  1 

08.2% 

00    7 

Organic  matter  insoluble  

.  2O 

1.8% 

.  £ 

Inorganic  matter 

OQ 

Trace 

Trace 

Bitumen   insoluble  in  88°  naphtha  
Bitumen  insoluble  in  CC14  
Fixed  carbon 

100.00 

19.3% 

0.0% 

ii  8% 

IOO.OO 

29.4% 
14.6% 

io  <;% 

100.00 

27.8 

6.0 
18  8% 

*  Taken  from  Richardson's  "  Modern  Asphalt  Pavement." 

In  regard  to  these  products  it  may  be  said  that  the  blown 
oil  and  asphaltic  pitch  might  be  used  to  advantage  in  road  con- 
struction, but  that  the  Semiasphaltic  pitch  is  too  hard,  as 
shown  by  its  penetration.  The  blown  oil  is  very  considerably 
softer  but  capable  of  hardening  with  age.  It  is  non- volatile  at 
163°  C.  but  increases  somewhat  in  consistency.  The  percent- 
age difference  in  penetration  of  the  residue  as  compared  with 
the  original  sample  is  not  so  pronounced  as  in  the  case  of  the 
California  pitch,  which  is  an  advantageous  feature  in  a  material 
of  sufficient  original  consistency  to  serve  as  a  strong  road  binder. 
It  has  been  carefully  prepared,  as  indicated  by  the  complete  sol- 
ubility of  its  bitumen  in  carbon  tetrachloride.  The  same  can 
hardly  be  said  for  the  asphaltic  pitch,  as  it  carries  six  per  cent 
insoluble  in  this  solvent.  The  Semiasphaltic  pitch  has  been 
quite  badly  cracked,  as  it  contains  1.8  per  cent  organic  matter 
insoluble  in  carbon  bisulphide  and  14.6  per  cent  insoluble  in 
carbon  tetrachloride. 

The  advantages  of  a  good  residual  pitch  over  a  blown  prod- 


PETROLEUM  AND  PETROLEUM  PRODUCTS       1/3 

uct  are  that  its  binding  power  is  greater,  it  shows  greater 
ductility  and  if  properly  prepared  is  less  subject  to  changes  by 
weathering.  A  blown  oil,  on  the  other  hand,  while  being  char- 
acteristically short  or  non-ductile,  is  less  susceptible  to  tempera- 
ture changes;  that  is,  at. extremes  of  heat  and  cold  its  physical 
properties  do  not  greatly  vary.  The  asphaltic  pitches,  if  mod- 
erately hard  at  ordinary  temperatures,  are  apt  to  be  brittle  in 
cold  weather  and  soft  in  hot  weather.  Under  proper  con- 
ditions both  materials  should  give  good  service  as  road  binders. 

Petroleum  Emulsions.  —  Emulsions  of  petroleum  with  water 
may  be  made  either  by  mechanical  or  chemical  means.  Chem- 
ical emulsions  have  been  most  generally  used  in  road  treat- 
ment, but  before  considering  them  it  may  be  well  to  mention 
an  apparatus  which  has  lately  been  devised  for  the  purpose  of 
forming  and  spreading  a  mechanical  mixture  of  oily  substances 
and  water  upon  a  road  surface.  This  is  a  cart  known  'as  the 
"Emulsifix,"  fitted  with  two  tanks,  one  containing  the  oil  and 
the  other  water.  These  two  substances  are  led  through  pipes 
into  a  box  where  they  are  thoroughly  mixed  by  means  of  rap- 
idly whirling  blades  which  also  force  the  mixture  upon  the 
road  in  the  form  of  a  fine  spray.  The  water  either  evaporates 
or  is  rapidly  absorbed  by  the  road,  leaving  the  oil  in  a  fine 
film  over  the  surface,  where  it  acts  as  a  dust  layer  and  tem- 
porary binder. 

Chemical  emulsions  are  oily  substances  made  miscible  with 
water  through  the  agency  of  saponifying  materials,  such  as 
caustic  soda,  potash  and  ammonia.  Petroleum  will  not  sapon- 
ify directly  to  any  extent  with  these  alkalies  and  recourse  must 
be  had  to  some  animal  or  vegetable  fat  which  will  react  with 
the  saponifying  agent  to  form  a  soap  solution  with  which  the 
mineral  oil  will  emulsify.  Commercial  oleic  acid,  known  as 
elaine,  and  cotton-seed  oil  are  most  commonly  employed  for 
this  purpose  to  the  extent  of  approximately  three  per  cent  by 
weight  of  the  oil.  Carbolic  acid,  pine  oil  and  various  other 
materials  are  sometimes  used  in  the  preparation  of  these  emul- 
sions both  for  the  purpose  of  assisting  the  process  of  emulsifica- 


174  DUST   PREVENTIVES    AND    ROAD    BINDERS 

tion  and  to  neutralize  or  destroy  any  objectionable  odor  which 
the  oil  may  have. 

In  1903  and  1904  road  oil  emulsions  first  made  their  appear- 
ance in  France  and  Germany  and  since  then  have  been  em- 
ployed to  some  extent  in  this  country.  They  are  sold  in 
concentrated  form  as  viscous,  oily  liquids  which  should  be  mixed 
with  a  considerable  amount  of  water  before  being  applied.  If 
they  contain  a  good  semiasphaltic  oil,  they  not  only  serve  as 
dust  layers,  but  as  semipermanent  binders,  and  as  they  have 
to  be  applied  at  frequent  intervals,  often  produce  an  accumu- 
lation of  oil  on  the  road  surface  which  binds  the  fine  particles  of 
roadstone  together  and  materially  protects  the  road  from  wear. 
If  the  oil  is  of  a  paraffin  nature,  however,  the  same  objections 
may  be  urged  against  its  use  as  were  made  in  connection  with 
the  use  of  crude  paraffin  oils,  the  only  difference  being  that 
when  emulsified  the  oil  may  be  applied  in  such  a  thin  coat 
that  the  undesirable  properties  are  not  so  obvious.  Such  emul- 
sions act  as  dust  layers  only  and  not  as  road  binders.  Some 
of  the  heavier  asphaltic  emulsions  have,  however,  been  sold 
as  permanent  binders  for  use  in  road  construction. 

An  objection  which  has  been  offered  to  the  use  of  petroleum 
oil  emulsions  is  that  being  originally  miscible  with  water  the 
oil  is  apt  to  be  washed  out  of  the  road  after  application  by 
rains.  This  is  true  to  only  a  limited  extent,  as  the  emulsified 
condition  is  a  very  unstable  one,  the  oil  and  water  being  in  a 
rather  delicate  state  of  equilibrium  which  may  be  readily  de- 
stroyed, thus  causing  a  separation  of  the  oil  and  water.  Pro- 
longed and  violent  agitation  will  cause  this  to  occur  and  also 
the  sudden  introduction  of  any  solid  matter  in  a  finely  divided 
state.  Thus  a  handful  of  sand  thrown  into  one  of  these  emul- 
sions will  often  cause  the  oil  and  water  to  separate  almost 
instantaneously  and  once  separated,  it  is  difficult  to  make  them 
mix  again.  It  is  very  probable  that  such  a  separation  takes 
place  when  an  emulsion  strikes  a  road  surface  and  this  would 
account  for  the  retention  of  the  oil  by  the  road  even  when 
subjected  to  long  spells  of  rain.  Because  of  this,  a  road  which 


PETROLEUM  AND  PETROLEUM  PRODUCTS 


175 


has  been  treated  for  a  season  with  a  good  emulsion  will  at  the 
end  of  that  time  often  have  the  appearance  of  having  been 
recently  treated  with  a  semipermanent  oil  binder.  Volatile 
emulsifying  agents  such  as  ammonia  are  to  be  preferred  to  the 
fixed  alkalies  not  only  because  a  more  complete  separation  is 
effected  upon  the  road  surface,  but  also  because  the  character 
of  the  oil  is  less  likely  to  be  injured. 

The  characteristics  of  two  typical  emulsifying  road  oils  are 
given  below: 

EMULSIFYING    ROAD    OILS. 


i 

2 

Characteristics 

Greasy 

Sticky 

Specific  gravity,  25°/25°  C    

0.023 

0.086 

Volatilization: 
Loss  at  room  temperature,  24  hours  

3.23% 

10.77% 

Additional  loss  at  100°  C.,  5  hours  

12.31% 

ii  .05% 

Character  of  residue 

Thick 

Semisolid 

Determinations  made  on  samples  dried  at  100°  C.  : 
Soluble  in  CS2,  air  temperature  

greasy, 
liquid 

07-  17% 

sticky 
07.08% 

Organic  and  other  volatile  matter  insoluble  

2.61% 

1.63% 

Inorganic  matter  non-volatile 

22% 

3Q% 

Insoluble  in  86°  naphtha,  air  temperature  

100.00 

q.oo% 

IOO.  OO 

10.68% 

Fixed  carbon  

1.17% 

r.2C% 

Remarks.  —  The  naphtha  insoluble  material  from  No.  i  was 
a  saponified  jelly  like  mass,  with  but  little  evidence  of  the  pres- 
ence of  residues  obtained  in  like  manner  from  asphaltic  oils. 
That  obtained  from  No.  2  was  asphaltic  in  character. 

From  the  above  results  it  is  evident  that  No.  2  is  greatly 
superior  in  road  binding  value  to  No  i.  The  former  contains 
an  excellent  semiasphaltic  oil  residuum,  while  the  latter  carries 
a  relatively  light  oil  very  rich  in  paraffin  hydrocarbons. 

In  some  instances  experimenters  have  prepared  oil  emulsions 
for  their  own  use  by  mixing  a  solution  of  common  soap  with  the 
oil  according  to  an  old  recipe  known  as  Cook's  formula.  The 


176  DUST   PREVENTIVES    AND    ROAD    BINDERS 

parkways  in  Boston  and  Chicago  have  for  the  last  few  years 
been  treated  with  such  emulsions  made  under  the  supervision 
of  the  park  superintendent.  In  the  former  case  ten  to  fifteen 
pounds  of  cotton-seed  oil  soap  are  first  dissolved  in  fifty  gallons 
of  water  by  the  aid  of  steam  heat.  To  every  fifty  gallons  of 
soap  solution  one  hundred  gallons  of  semiasphaltic  oil  are  added 
and  emulsified  through  agitation  by  a  steam  pump.  This  forms 
a  stock  solution  containing  66  per  cent  of  petroleum,  which  is 
further  diluted  with  water  before  application. 

In  Lincoln  Park,  Chicago,  a  mixture  of  Kansas  and  Cali- 
fornia oils  is  emulsified.  In  this  case  a  naphtha  soap  is  em- 
ployed because  it  is  found  to  work  best  with  the  hard  lake 
water.  The  process  of  emulsification  is  described  by  West  *  as 
follows:  "The  mixing  plant  consists  of  a  series  of  three  two- 
hundred-gallon  hogsheads,  set  close  together  on  end  with  their 
top  heads  removed.  The  hogsheads  are  connected  at  the  bot- 
tom with  three-inch  pipe  having  gate  valves.  In  each  of  these 
receptacles  are  pipes  for  live  steam  and  for  cold  water.  From 
the  bottom  of  the  hogsheads  connecting  pipes  lead  to  a  steam 
pump  of  about  forty  gallons  capacity.  Arrangements  are  made 
so  that  the  material  can  be  pumped  through  any  one  of  the 
hogsheads  back  into  the  same  or  other  compartments  through  a 
reduced  nozzle ;  or  so  that  the  material  may  be  pumped  from  the 
oil  delivery  wagon  to  any  of  the  receptacles;  or  from  any  of  the 
receptacles  into  a  sprinkler,  which  is  used  in  applying  the  emul- 
sion to  the  road. 

"In  making  the  emulsion,  sixty  gallons  of  water  are  drawn 
into  two  of  the  hogsheads,  the  third  hogshead  being  discon- 
nected and  reserved  for  heating  water  for  subsequent  use. 
Live  steam  is  then  turned  on,  and  the  water  brought  to  its  boil- 
ing point.  Fifteen  pounds  of  soap  are  then  added  and  the 
water  allowed  to  boil  five  minutes  longer.  Sixty  gallons  of 
the  Kansas  oil  are  then  added,  and  the  mixture  allowed  to  pass 
out  of  the  bottom  of  one  hogshead,  through  the  steam  pump 
back  into  the  top  of  hogshead  number  two,  through  the  agi- 

*  Good  Roads  Magazine,  November,  1907.  "Oil  Emulsions  for  Macadam  Roads." 


PETROLEUM  AND  PETROLEUM  PRODUCTS      I// 

tating  hose  for  about  five  minutes,  when  one-half  barrel  of 
California  asphaltum  is  added,  and  the  whole  mixture  allowed 
to  emulsify  for  twenty  minutes  longer.  It  is  then  pumped  into 
a  distributing  sprinkler  of  eight  hundred  gallons  capacity,  fitted 
with  an  adjustable  cup  discharging  attachment.  After  receiv- 
ing the  stock  solution  the  sprinkler  is  filled  to  its  capacity  with 
boiling  water." 

Summary  and  Conclusions.  —  In  this  chapter  the  production 
and  characteristics  of  petroleums,  together  with  their  products 
of  manufacture  which  are  of  interest  from  the  standpoint  of 
road  treatment,  have  been  reviewed.  The  supply  of  petroleum 
being  at  the  present  time  almost  unlimited  and  the  properties  of 
many  of  these  oils  being  suitable  for  this  purpose,  it  is  evident 
that  oil  and  oil  products  will  for  a  long  time  continue  to  be  an 
important  factor  in  dust  prevention  and  road  preservation.  As 
the  properties  of  different  oils  vary  within  wide  limits  and  as 
some  are  totally  unfit  for  road  purposes,  it  is  most  necessary  that 
an  examination  or  analysis  be  made  before  selecting  a  product 
for  any  considerable  amount  of  work.  The  use  of  oils  and  their 
methods  of  examination  are  treated  in  other  chapters,  which 
should  be  closely  associated  in  the  reader's  mind  with  the  fore- 
going in  order  to  obtain  a  correct  idea  of  the  value  of  results 
of  the  analyses  as  given  in  the  preceding  tables. 


CHAPTER  IX. 
SEMISOLID  AND   SOLID   NATIVE  BITUMENS. 

THE  semisolid  and  solid  native  bitumens  of  interest  from 
the  standpoint  of  road  treatment  include  the  natural  malthas, 
so-called  rock  asphalts,  genuine  asphalts,  gilsonite  and  graham- 
ite.  As  a  class  they  represent  the  most  permanent  type  of 
road  binders,  but  only  serve  as  dust  preventives  by  reducing 
the  wear  of  roads  in  which  they  are  employed.  Some  of  them 
have  been  employed  for  many  years  in  the  construction  of 
sheet  asphalt  pavements.  It  does  not  come  within  the  scope 
of  this  book  to  consider  them  in  this  connection,  and  as  a  num- 
ber of  standard  textbooks  dealing  with  the  construction  of  this 
type  of  pavement  have  been  published,  it  is  unnecessary  to  so 
treat  them.  Their  adaptability  for  road  treatment  and  con- 
struction especially  will,  therefore,  be  made  the  subject  of  this 
chapter.  It  should  be  remembered,  however,  that  their  use  for 
this  purpose  is  the  connecting  link  between  the  suburban  road 
and  the  city  pavement,  and  an  overlapping  of  the  two  subjects 
at  this  point  is  almost  inevitable  as  no  sharp  dividing  line  can 
be  drawn  between  them. 

Malthas.  —  Malthas  or,  as  they  are  sometimes  called,  mineral 
tars,  are  very  viscous  semiasphaltic  or  asphaltic  substances,  hold- 
ing, as  has  been  stated,  an  intermediate  position  between  the 
petroleums  of  an  asphaltic  nature  and  the  true  asphalts.  Some 
are  probably  the  direct  products  of  natural  distillation  of  organic 
materials  and  some  have  been  formed  by  the  natural  evapora- 
tion and  oxidation  of  certain  petroleums.  They  are  usually 
black  or  brown  black  in  color  and  range  in  specific  gravity 
from  0.95  to  i. oo  and  slightly  higher.  Some  are  so  nearly  solid 
that  they  can  be  drawn  into  threads.  They  resemble  certain 

178 


SEMISOLID    AND    SOLID   NATIVE   BITUMENS 

artificial  petroleum  residuums  in  some  respects  but  contain 
a  larger  proportion  of  volatile  hydrocarbons,  and  when  moder- 
ately heated  are  converted  into  harder  material.  Because  of  this 
they  are  little  suited  for  use  as  fluxes  for  the  harder  bitumens 
but  should  prove  serviceable  in  the  treatment  of  roads,  as 
their  binding  qualities  improve  with  age  under  service  conditions. 
They  are  in  fact  slowly  transformed  into  a  species  of  asphalt 
upon  exposure  to  the  atmosphere  both  by  evaporation  and 
oxidation. 

Most  of  the  maltha  exploited  in  this  country  is  found  in  Cali- 
fornia. During  1908  this  state  produced  12,579  short  tons 
valued  at  $158,520  out  of  a  total  for  the  United  States  of  12,875 
tons  valued  at  $162,000.  Oklahoma  produced  the  remaining  116 
tons  valued  at  $3 ,480.  There  is  little  data  to  be  had  relative  to 
the  physical  and  chemical  characteristics  of  the  malthas,  but  the 
following  analysis  of  a  California  product  as  given  by  Richard- 
son *  gives  some  idea  of  their  general  properties. 

CALIFORNIA    MALTHA. 

Specific  gravity,  2^/25°  C 0.9867 

Flash  point,  degrees  C 1 18° 

Loss  at  163°  C.,  7  hours 7 .  o% 

Loss  at  205°  C.,  7  hours 28.0% 

Penetration  of  residue 40° 

Bitumen  insoluble  in  88°  naphtha 6.7% 

The  malthas  often  contain  gas  and  water  and  when  heated 
froth  violently.  According  to  Peckham  some  of  the  water 
appears  to  be  chemically  combined  as  water  of  hydration  of 
certain  basic  oils  present  in  the  maltha.  This,  however,  has 
not  been  definitely  proven. 

Rock  Asphalts.  —  Rock  asphalt  or  bituminous  rock  is  the 
term  applied  to  a  great  variety  of  sandstones  and  limestones 
more  or  less  saturated  with  maltha.  In  reports  of  the  Geo- 
logical Survey  it  is  also  made  to  apply  to  asphaltic  earths  and 
shales.  The  rock  may  be  either  friable  and  wholly  dependent 

*  "The  Modern  Asphalt  Pavement,"  Second  Edition,  p.  129. 


ISO  DUST   PREVENTIVES   AND    ROAD   BINDERS 

upon  the  bitumen  to  hold  the  individual  mineral  fragments 
together  or  it  may  be  solid,  merely  having  its  interstices  filled 
with  bitumen.  Deposits  of  such  materials  are  widely  distributed 
over  the  United  States,  but  are  found  principally  in  California 
and  Kentucky.  The  output  in  short  tons  in  1908  for  these 
states  was  as  follows : 

PRODUCTION    OF    BITUMINOUS    ROCK    IN    1908. 


State. 

Quantity. 

Value. 

California  

27  118 

Kentucky  

IO  2^3 

3w"O 

Total 

$146  821 

6h6l  L 

Taff*  describes  the  occurrence  of  bituminous  rock  in  the 
United  States  as  follows: 

"  Extensive  deposits  of  asphaltic  shale  and  sandstone  are 
found  in  California  in  and  contiguous  to  the  oil  fields  from  the 
vicinity  of  Santa  Cruz  south  westward,  generally  parallel  with 
the  coast.  Bitumen  permeates  porous  sandy  strata  and  exudes 
at  the  surface  from  highly  bituminous  oil-bearing  deposits, 
and  is  found  in  smaller  quantities  in  veins  cutting  the  same 
class  of  rocks.  The  asphalt  in  this  region  appears  for  the  most 
part  to  be  a  residue  by  natural  distillation  at  or  near  the  sur- 
face of  the  earth  from  the  same  crude  oil  that  yields  the  oil 
asphalt. 

"Utah  contains  large  deposits  of  both  asphaltic  limestone  and 
sandstone.  Those  probably  of  greatest  purity  and  highest 
quality  are  the  asphaltic  limestones  in  the  vicinity  of  Indian  and 
Lake  canyons  in  Strawberry  Creek  valley,  Wasatch  County; 
on  Tie  Fork  of  Soldier  Creek  northwest  of  Tucker,  on  the  Rio 
Grande  Western  Railroad,  Utah  County;  and  between  Soldier 
and  Diamond  creeks,  a  few  miles  northeast  of  Thistle  Junction, 

*  "  Mineral  Resources  of  the  United  States,  Calendar  Year  1908."  U.  S.  Geo- 
logical Survey, 


SEMISOLID    AND    SOLID   NATIVE   BITUMENS  l8l 

in  the  same  county.  Bituminous  rock  deposits  are  also  reported 
from  the  same  vicinities  south  of  Thistle  Junction.  Similar 
deposits  of  bituminous  limestone  are  known  near  the  head  of 
Whittemore  Canyon  north  of  Sunnyside,  in  Carbon  County. 
In  the  Strawberry  Creek  valley  especially  the  bituminous  rock 
seems  to  be  associated  with  veins  of  wurtzelite,  and  it  is  probable 
that  the  asphalt  contained  in  the  limestone  partakes  of  the 
nature  of  wurtzelite  or  gilsonite.  The  natural  asphalt  that 
exudes  from  the  bituminous  rock  of  certain  localities  in  Wasatch 
and  Carbon  counties  is  noticeably  tenacious  and  elastic.  Bitumi- 
nous sandstone  is  reported  in  Uinta  County  east  and  northwest 
of  Jensen,  and  in  the  Book  Cliffs  toward  the  source  of  Willow 
and  Whittemore  creeks  in  Carbon  County.  These  bituminous- 
rock  deposits  are  flat  lying  and  are  usually  accessible  from  the 
sides  of  the  canyon  and  valleys.  All  the  bituminous-rock 
deposits  of  Utah  at  present  known  are  contained  in  formations 
of  Tertiary  or  later  age,  and  occur  in  or  near  the  boundaries 
of  the  Uinta  Basin. 

"  Extensive  deposits  of  bituminous  rock  of  variable  richness  are 
found  in  Oklahoma.  Flat-lying  strata  of  bituminous  sand  occur 
in  eastern  Stephens,  in  Jefferson,  in  Comanche  and  in  Carter 
counties  in  late  Carboniferous  strata.  Notable  deposits  also 
occur  near  Loco  and  Asphaltum,  and  asphaltic  sandstones, 
more  or  less  steeply  inclined,  are  found  in  Carboniferous  rocks 
near  Woodford,  Ardmore,  Overbrook,  Buckhorn  and  Fitzhugh. 
Bituminous  sandstone  and  limestone  in  large  quantity  and  of 
considerable  richness,  impregnating  rocks  of  Ordovician  age, 
are  found  at  Gilsonite  and  near  Sulphur  and  Dougherty,  in 
Murray  County. 

"Bituminous  rock  is  found  in  Texas  as  asphaltic  sand  and 
limestone,  occurring  in  the  basal  Comanche  rocks  in  Burnett 
County,  near  the  town  of  Burnett,  and  in  Montague  County, 
near  St.  Joe;  as  asphaltic  limestone  of  Cretaceous  age  in  Nueces 
County ;  and  as  asphaltic  limestone  in  Uvalde  County  —  which 
appears  to  be  of  better  quality  and  of  more  interest  at  the 
present  time  than  the  bituminous  sandstone  found  elsewhere  in 


1 82  DUST   PREVENTIVES    AND    ROAD    BINDERS 

Texas.  This  limestone  is  very  porous,  and  the  interstices  and 
cavities  contain  a  semisolid  asphalt. 

"  The  asphalts  of  Kentucky  occur  as  bituminous  impregnations 
of  flat-lying  Carboniferous  sandstones,  chiefly  in  the  western 
part  of  the  state,  in  Breckenridge,  Grayson,  Edmonson,  Warren 
and  Logan  counties,  and  in  Carter  and  Floyd  counties  in  the 
northeastern  part. 

"Asphaltic  sandstone  of  possible  commercial  value  is  found 
in  southwestern  Wyoming  in  Sec.  15,  T.  15  N.,  R.  118  W. 
This  bed  is  six  feet  thick,  and  its  areal  extent  is  not  known. 
Another  asphaltic  sandstone  of  similar  quality  and  of  the  same 
thickness  occurs  in  the  Bighorn  Basin,  in  northern  Wyoming, 
Sees.  28,  29,  32,  and  33,  T.  52  N.,  R.  89  W. 

"  Asphaltic  sands  of  Comanche  (Lower  Cretaceous)  age  occur 
in  Arkansas  near  Wolf  Creek,  Pike  County.  Bituminous  sand- 
stones of  Carboniferous  age  have  been  developed  locally  in 
Missouri  in  the  vicinity  of  Higgins  Valley,  Lafayette  County, 
and  in  northern  Alabama,  but  their  commercial  values  are  not 
known.  Bituminous  rock  in  Georgia  has  been  reported  from 
Fulton  County.  Presumably  for  trade  reasons,  bituminous  de- 
posits are  not  exploited  in  these  states  at  the  present  time." 

Rock  asphalt  has  been  employed  to  a  considerable  extent  in 
the  surfacing  of  macadam  roads,  but  it  is  not  all  suitable  for 
this  purpose  as  both  the  character  and  percentage  of  bitumen 
present  vary  within  rather  wide  limits.  Thus  some  are  com- 
paratively solid  rock  carrying  only  one  or  two  per  cent  of 
maltha,  while  others  are  loosely  compacted  sand  deposits,  the 
individual  grains  of  which  are  bound  together  by  the  bitumen, 
which  may  run  from  three  to  nineteen  per  cent.  The  maltha 
itself  may  be  either  semiasphaltic  or  asphaltic,  the  latter  of  course 
being  preferable.  When  separated  from  the  bitumen  the  mineral 
aggregate  will  also  vary  greatly  in  different  specimens.  As  a 
rule  it  is  not  properly  graded  for  the  construction  of  sheet 
asphalt  surfaces  and  the  bitumen  is  seldom  of  the  right  con- 
sistency for  this  purpose.  As  the  serviceability  of  a  sheet 
asphalt  wearing  surface  is  dependent  upon  the  grading  of  the 


SEMISOLID   AND    SOLID   NATIVE    BITUMENS  183 

aggregate,  the  consistency  of  the  bituminous  binder  and  the  per- 
centage of  this  binder  within  comparatively  narrow  limits,  it  is 
evident  that  the  occurrence  of  a  suitable  combination  of  these 
properties  in  nature  must  be  rather  exceptional.  For  road  work, 
however,  the  limitations  are  much  broader  and  many  of  the  rock 
asphalts  may  be  employed  to  advantage. 

Kentucky  rock  asphalt  has  been  quite  extensively  exploited 
in  the  last  few  years  for  use  in  macadam  construction  and  in 
many  cases  has  produced  excellent  results.  It  is  a  fine  grained 
sandstone  impregnated  with  a  sticky  semiasphaltic  maltha  aver- 
aging from  6  to  8  per  cent  with  a  maximum  of  12  per  cent.  It 
is  found  in  pockets  rather  than  in  direct  continuous  veins,  the 
distribution  of  the  bitumen  throughout  the  pocket  ranging  from 
a  mere  trace  to  saturation. 

The  quarrying  and  first  crushing  of  rock  asphalt  are  not 
unlike  that  of  other  rocks  intended  for  macadam  work.  After 
being  broken  in  pieces  to  pass  a  two-inch  ring,  it  is  conducted 
to  a  series  of  roll  crushers,  consisting  of  parallel  steel  cylinders, 
the  bitumen  in  the  rock  producing  sufficient  adhesion  to  carry 
the  material  through  the  rolls  once  it  has  been  forced  against 
them.  The  finished  product  after  crushing  should  consist  of 
an  aggregation  of  individual  grains  of  sand,  each  thoroughly 
coated  with  a  film  of  bitumen  which  should  cause  it  to  adhere 
firmly  to  the  surrounding  grains  if  subjected  to  pressure.  If 
chilled  after  compaction  the  mass  becomes  very  hard  and  tough. 
If  warmed  in  the  hand  the  bitumen  becomes  semifluid  and  the 
whole  mass  mobile.  It  is  this  property  which  makes  it  pos- 
sible to  apply  rock  asphalt  in  warm  weather  as  a  binder  for  a 
macadam  road.  With  age  the  bitumen  hardens  into  a  more 
asphalt-like  substance  in  the  same  way  that  all  malthas  harden 
when  exposed  to  the  atmosphere. 

The  properties  of  a  rock  asphalt  suitable  for  road  purposes 
are  shown  in  the  following  table,  and  the  application  of  such 
material  will  be  described  in  the  succeeding  chapter. 


1 84  DUST  PREVENTIVES   AND   ROAD   BINDERS 

KENTUCKY    ROCK    ASPHALT. 

Bituminous  material  removed  by  CS2,  air  temperature 6.  73% 

Mineral  aggregate 93 . 27% 

Retained  on    10  mesh  sieve   i .  o 

"       "     20      "         "      3.0 

"       "     30      "         "      5.5 

"     50      "         "      43-° 

"       "     8o      "         "      35 -° 

"       "    ioo       "         "       4-5 

"  "200         "  " 4.5 

Passing  200  mesh  sieve 3.5 

100.0 

Specific  gravity,  bituminous  material,  2$°/2$°  C i  027 

Character viscous,  sticky 

Loss  at  163°  C.,  5  hours 5 . 41% 

Character  of  residue semisolid,  sticky 

Bitumen  soluble  in  CS2,  air  temperature 98. 24% 

Organic  material  insoluble oo 

Inorganic  material 1.76 


100.00 

Per  cent  of  bitumen  insoluble  in  86°  naphtha 17.9% 

Fixed  carbon 10-83 

Asphalts.  —  The  true  asphalts  and  other  solid  native  bitumens 
of  an  asphaltic  nature  are  of  interest  in  the  treatment  of  roads 
only  in  combination  with  bitumens  of  a  fluid  nature.  They  are 
too  hard  to  be  employed  in  their  natural  state  but  when  fluxed 
with  the  proper  amount  of  a  suitable  oil  residuum,  produce 
asphaltic  cements  of  excellent  binding  character. 

Natural  asphalts  do  not  occur  in  the  United  States  to  any 
great  extent,  but  small  quantities  are  found  in  California  and 
have  in  the  past  been  exploited.  The  greater  part  of  the  as- 
phalt imported  to  the  United  States  comes  from  Trinidad 
although  considerable  quantities  come  from  Bermudez,  and 
smaller  amounts  from  Maricaibo,  Cuba  and  Mexico.  Domes- 
tic oil  asphalts  are  supplanting  them  to  some  extent  and  com- 
petition is  keen  owing  to  the  lower  price  although  sometimes 
inferior  quality  of  the  domestic  product.  Imported  asphalts 
are  for  the  most  part  employed  in  the  construction  of  street 


SEMISOLID   AND   SOLID   NATIVE  BITUMENS  185 

pavements  although  lately  some  attempt  has  been  made  to 
utilize  them  for  road  work. 

Trinidad  asphalt  occurs  in  two  forms,  known  as  lake  pitch 
and  land  pitch,  which  differ  somewhat  in  properties  but  origi- 
nate from  the  same  source.  The  lake  pitch  occupies  what  is 
thought  to  be  the  crater  of  an  extinct  mud  volcano  while  the 
land  pitch  occurs  in  layers  which  were  supposedly  produced  by 
overflows  from  the  lake.  The  pitch  lake  has  an  area  of  some- 
thing over  100  acres  and  is  of  unknown  depth.  Borings  have 
been  made  to  a  depth  of  135  feet  at  the  center  with  no  indication 
of  having  reached  the  bottom  of  the  deposit.  The  estimated 
minimum  available  tonnage  of  asphalt  in  this  lake  is  9,000,000 
tons.  During  1908  over  92,000  tons  of  this  material  were 
imported  into  the  United  States  together  with  nearly  6,000  tons 
of  land  pitch. 

The  crude  lake  asphalt  is  a  uniform  cheesy  mixture  of  gas, 
water,  fine  sand,  clay  and  bitumen,  carrying  about  39  per  cent 
of  the  latter  constituent.  It  flows  slowly  and  excavations  made 
in  the  lake  gradually  fill  up.  In  the  refined  product  the  bitu- 
men amounts  to  about  56  per  cent  and  is  a  black,  lustrous  pitch 
having  a  specific  gravity  of  1.06  to  1.07.  It  contains  a  large 
percentage  of  sulphur  and  some  nitrogen,  but  little  or  no  oxy- 
gen. In  common  with  other  asphalts  no  solid  paraffins  are 
present  but  saturated  hydrocarbons  of  the  CnH2n_2  series  have 
been  found.  Polycyclic  polymethylenes  similar  to  those  con- 
tained in  the  asphaltic  oils  are  present  in  the  lighter  portions 
soluble  in  petroleum  ether,  and  extremely  complex  unsatu- 
rated  hydrocarbons  make  up  the  bulk  of  the  naphtha  insoluble 
material.  Further  physical  and  chemical  characteristics  of  this 
and  other  asphalts  will  be  found  in  the  table  of  solid  native 
bitumens  on  page  191. 

Trinidad  land  asphalt  differs  from  the  lake  product  in  the 
fact  that  it  is  very  much  weathered  being  denser  and  harder 
than  the  latter.  It  is  of  much  less  importance  commercially 
and  need  not  be  considered  further  than  to  state  that  the  addi- 
tion of  about  fifty  per  cent  more  of  a  given  flux  is  required  to 


1 86  DUST   PREVENTIVES    AND    ROAD    BINDERS 

bring  it  to  the  consistency  of  an  ordinary  asphaltic  cement 
than  in  the  case  of  the  lake  pitch.  It  is  not  as  uniform  as  the 
lake  product  and  has  not  proved  as  serviceable. 

Bermudez  asphalt  is  obtained  from  a  shallow  pitch  lake 
formed  by  the  overflow  of  soft  pitch  from  several  springs.  The 
asphalt  hardens  slowly  upon  exposure  and  evolves  gas.  It 
does  not,  however,  retain  as  much  of  this  gas  as  the  Trinidad 
product  and  carries  a  much  smaller  quantity  of  mineral  matter. 
In  fact  the  original  pitch  as  it  exudes  from  the  springs  is  an 
extremely  pure  bitumen.  It  contains  sulphur  but  in  less  quan- 
tity than  the  Trinidad.  The  deposit  extends  over  an  area  of 
nearly  1000  acres  and  is  in  many  places  covered  with  a  rank 
vegetable  growth  which  is  burned  from  time  to  time  and  conse- 
quently hardens  the  asphalt  in  its  vicinity.  The  crude  material 
as  it  is  taken  from  the  deposit  carries  from  10  to  46  per  cent  of 
water,  from  0.5  to  3.6  per  cent  mineral  matter  and  from  0.6  to 
6  per  cent  adventitious  organic  matter,  gas,  etc.  The  refined 
asphalt  varies  in  character  to  a  greater  extent  than  the  Trinidad 
product.  It  contains  about  the  same  percentage  of  unsatu- 
rated  hydrocarbons  as  the  latter  but  a  higher  percentage  of 
volatile  constituents.  There  has  in  the  past  been  much  dis- 
cussion as  to  the  relative  merits  of  the  two  asphalts  for  street 
paving.  Both  materials  when  properly  employed  have  pro- 
duced excellent  pavements  and  in  many  respects  there  is  little 
choice  to  be  made  in  favor  of  one  or  the  other.  This  is  certainly 
true  as  regards  road  work  where  the  refinements  of  construction 
in  city  paving  are  not  encountered.  It  is  improbable  that 
either  asphalt  will  ever  be  extensively  employed  for  this  pur- 
pose owing  to  their  high  cost  and  to  the  fact  that  the  cheaper 
domestic  oil  asphalts  and  tar  pitches  will  be  found  satisfactory. 

Other  varieties  of  asphalt  such  as  the  Maracaibo,  Cuban, 
Mexican  and  California  are  of  minor  importance  compared  with 
the  Trinidad  and  Bermudez  products.  Their  approximate 
characteristics  are,  however,  shown  in  the  table  of  the  solid 
native  bitumens.  None  of  these  materials  are  likely  to  play  an 
important  role  as  dust  preventives  or  road  binders  in  this 


SEMISOLID    AND    SOLID    NATIVE    BITUMENS  l8/ 

country  and  they  are  mentioned  as  being  only  of  passing  in- 
terest. They  all  possess  excellent  road  binding  characteristics 
and  may  undoubtedly  be  employed  to  advantage  in  localities 
near  which  they  are  found. 

Asphalt  Refining.  —  Before  they  can  be  used  commercially  > 
crude  asphalts  must  be  treated  for  the  removal  of  water  and 
other  impurities.  This  is  accomplished  in  a  very  simple  manner 
by  heating  the  asphalt  until  the  water  and  gases  have  been 
driven  off,  skimming  off  any  vegetable  matter  which  may  rise 
to  the  surface  of  the  melted  material  and  in  some  cases  removing 
the  coarser  mineral  particles  which  may  settle  to  the  bottom. 
Some  of  the  more  volatile  hydrocarbons  are  also  removed  by 
this  treatment.  When  the  mineral  matter  is  in  a  very  finely 
divided  state  and  difficult  to  remove  as  in  the  case  of  Trinidad 
asphalt,  it  is  allowed  to  remain,  and  acts  as  a  filler  in  the  con- 
struction of  sheet  asphalt  pavements.  While  it  may  prove  of 
service  for  this  purpose,  it  can  only  be  considered  as  a  natural 
adulterant,  of  little  or  no  value  in  connection  with  road  work 
where  no  particular  attempt  is  made  to  reduce  the  voids  to 
a  minimum. 

.  The  refining  process  is  conducted  in  two  ways  known  as  the 
fire  method  and  the  steam  method.  In  the  former,  the  crude 
material  is  placed  in  an  open  iron  tank  or  melting  kettle  resting 
upon  an  arch  of  brick  and  heated  by  means  of  a  free  fire.  In  the 
steam  method  the  asphalt  is  heated  with  superheated  steam  in 
a  large  rectangular  tank  fitted  with  coils  or  gangs  of  pipe.  By 
this  means  the  temperature  of  the  asphalt  can  be  readily  con- 
trolled and  the  danger  of  overheating  and  cracking  by  the  fire 
method  is  overcome.  In  either  case  the  mass  is  kept  agitated  by 
a  current  of  air  or  steam.  When  all  the  water  has  been  driven 
off  the  process  of  refining  is  finished  and  the  melted  asphalt 
is  drawn  off  into  barrels  which  have  been  clayed  on  the  inside 
to  prevent  it  from  sticking.  This  makes  it  possible  to  strip  off 
the  staves  without  difficulty  when  being  used.  About  four 
days  are  required  to  complete  the  refining  operation  by  the  fire 
method  and  cracking  is  never  entirely  prevented  no  matter  how 


1 88  DUST   PREVENTIVES    AND    ROAD   BINDERS 

carefully  the  kettle  has  been  fired.  The  steam  method  on  the 
other  hand  consumes  only  twenty-four  hours.  If  air  is  employed 
for  the  purpose  of  agitation  a  condition  of  affairs  very  similar 
to  that  described  under  blown  oils  is  brought  about  and  as 
might  be  expected  certain  oxidized  and  condensed  hydrocarbons 
are  formed  which  may  strongly  affect  the  character  of  the  prod- 
uct. Steam  agitation  on  the  other  hand  causes  the  volatiliza- 
tion of  a  larger  proportion  of  the  lighter  hydrocarbons. 

Gilsonite.  —  Gilsonite  is  a  very  pure  solid  native  bitumen, 
having  a  specific  gravity  of  from  1.044  to  1.049.  It  is  the  most 
abundant  of  all  of  the  solid  native  bitumens  found  in  the  United 
States,  but  its  occurrence  in  commercial  quantities  is  apparently 
limited  to  Utah  and  Colorado.  It  is  found  principally  in  the 
former  state  and  is  sometimes  called  Utah  asphalt.  In  1908 
this  state  produced  18,533  short  tons  valued  at  $61,824. 

It  is  differentiated  from  the  natural  asphalts  by  being  almost 
entirely  soluble  in  carbon  bisulphide  and  showing  the  presence 
of  but  little  mineral  matter.  It  is  more  brittle  than  the  asphalts 
and  much  less  soluble  in  86  °  B.  naphtha.  It  also  has  a  higher 
softening  or  melting  point.  The  lighter  products  contained  in 
gilsonite  are  composed  almost  entirely  of  unsaturated  compounds, 
while,  as  has  been  stated,  the  corresponding  constituents  of  the 
asphalts  are  for  the  most  part  saturated  hydrocarbons. 

Gilsonite  has  been  successfully  employed  in  the  paving 
industry  and  is  of  considerable  interest  from  the  standpoint  of 
road  treatment,  as  a  number  of  road  preparations  are  now  upon 
the  market  which  contain  it  as  a  binding  base.  It  of  course  has 
to  be  combined  with  an  oil  flux  before  it  can  be  made  suitable 
for  use  in  this  connection.  Being  an  extremely  pure  bitumen 
it  does  not  have  to  be  refined,  but  is  disposed  of  just  as  it  is 
taken  from  the  veins  in  which  it  occurs.  It  is  sold  in  two 
grades,  firsts  and  seconds,  the  former  consisting  of  large  lumps 
free  from  powder  and  the  latter  of  smaller  and  more  powdery 
material.  It  is  employed  to  a  considerable  extent  in  the  manu- 
facture of  japans,  paints,  varnishes,  electric  insulations,  acid 
fume  proofing,  etc.  where  it  is  prized  for  the  smooth,  elastic, 


SEMISOLID   AND   SOLID   NATIVE   BITUMENS  189 

resistant  and  durable  coating  which  it  produces.  Its  physical 
and  chemical  properties  are  shown  in  the  table  of  solid  native 
bitumens. 

Grahamite.  —  Grahamite  like  gilsonite  is  a  very  pure  solid  native 
bitumen.  It  is  black  and  brittle  and  does  not  melt  readily  but 
intumesces  at  high  temperatures.  It  is  found  almost  exclusively 
in  Oklahoma,  although  a  small  quantity  has  been  found  in  Colo- 
orado.  It  was  first  discovered  in  West  Virginia  but  the  avail- 
able supply  in  this  state  has  become  exhausted.  In  1908,  2,286 
short  tons  valued  at  $20,340  were  produced  in  Oklahoma. 

Grahamite  is  differentiated  from  gilsonite  and  the  native 
asphalts  by  the  fact  that  it  is  almost  completely  insoluble  in 
naphtha.  It  is  far  less  soluble  in  carbon  tetrachloride  than 
either  of  the  other  classes  of  material,  which  as  in  the  case  of 
oil  pitches  is  an  indication  that  high  temperatures  have  played 
an  important  part  in  its  production.  It  is  not  as  uniform  in 
composition  as  gilsonite,  and  some  varieties  approach  very 
closely  the  pyrobitumens  in  character  and  are  known  as  asphaltic 
coals.  It  is  probably  composed  almost  entirely  of  unsaturated 
hydrocarbons. 

Some  varieties  of  grahamite  have  proved  satisfactory  in 
paving  work  when  properly  fluxed,  and  good  results  would 
probably  be  obtained  by  its  use  in  road  construction,  although 
to  the  author's  knowledge  it  has  never  been  employed  to  any 
extent  for  this  purpose.  It  has  been  used  in  the  manufacture 
of  paints,  rubber  substitutes  and  fillers  for  brick  and  block 
pavements. 

Comparison  of  the  Solid  Native  Bitumens.  —  Some  of  the 
differences  between  the  various  types  of  solid  native  bitumens 
have  already  been  noted,  but  before  leaving  this  subject  it  may 
be  well  to  consider  these  differences  in  greater  detail  as  they  often 
have  a  direct  bearing  upon  the  proper  method  of  preparing  and 
handling  mixtures  suitable  for  paving  and  road  work.  The 
approximate  chemical  and  physical  properties  given  in  the  table 
on  page  191  have  been  taken  from  reports  on  the  examination  of 
typical  samples  of  the  various  materials,  and  show  the  principal 


190  DUST   PREVENTIVES   AND    ROAD   BINDERS 

differences  as  effecting  their  use  for  the  purposes  above  men- 
tioned. It  should,  however,  be  remembered  that  the  solid 
native  bitumens  must  always  be  modified  before  use  and  that 
by  treating  in  a  slightly  different  manner,  materials  which  are 
originally  quite  dissimilar,  can  often  be  made  into  finished 
products  exhibiting  very  similar  properties. 

In  this  table  it  will  be  noticed  that  the  specific  gravities  of  the 
solid  native  bitumens  are  for  the  most  part  dependent  upon  the 
amount  of  mineral  matter  which  they  contain.     Thus  Trinidad 
asphalt   carries  the  highest   per  cent  of   mineral  matter  and 
has  a  specific  gravity  of  1.40,  while  gilsonite  being  a  practically 
pure  bitumen  has  a  specific  gravity  of  only  1.04.     The  other 
materials  fall  into  line  between  these  two  almost  in  the  order  of 
their  decreasing  mineral  matter  contents  or  as  their  solubility 
in  carbon  bisulphide  increases.     Although  not  shown  in   the 
table,  it  should  be  noted  that  the  fracture  of  grahamite  differs 
materially  from  all  of  the  rest,  being  hackley  while  the  others 
show  a  conchoidal  or  semiconchoidal  fracture.      The  loss  by 
volatilization  at  163°  C.  and  205°  C.  is  low  in  nearly  every  case 
but  that  of  the  Mexican  asphalt.     This  would  naturally  be 
expected  in  any  solid  bitumen.     The  penetration  results  show 
that  Bermudez  has  a  little  softer  consistency  than  Trinidad,  and 
that  the  Mexican  is  much  softer  than  any  of  the  others.     The 
reason  for  this  is  apparent  in  their  greater  volatility.     The  per 
cent  of  bitumen  soluble  in  88°  B.  naphtha  is  found  to  vary 
considerably  among  the  different  materials,  falling  from  75  per 
cent  in  case  of  the  Mexican  asphalt  to  practically  zero  in  the 
case  of  grahamite,  which  is  characteristic  of  the  latter.     These 
naphtha  soluble    bitumens   have   been    termed   malthenes  by 
Richardson  and  the  naphtha  insoluble,  asphaltenes.     The  signifi- 
cance of  these  terms  will  be  discussed  in  a  later  chapter,  but  for 
the  present  it  may  be  said  that  the  relation  of  one  to  the  other 
will  often  have  a  very  important  bearing  upon  the  treatment  of 
solid  bitumens  in  the  preparation  of  asphaltic  cements.     The 
amount  of  unsaturated  hydrocarbons  present  in  the  naphtha 
soluble  bitumen  has  been  found  to  lie  between  50  and  60  per 


SEMISOLID   AND   SOLID  NATIVE   BITUMENS 


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DUST   PREVENTIVES   AND    ROAD   BINDERS 

cent  in  nearly  every  case  but  that  of  gilsonite,  which  is  character- 
istically high,  being  about  82  per  cent.  The  carbon  tetra- 
chloride  insoluble  material  is  low  in  every  case  but  that  of 
grahamite  which  is  an  indication  that  only  the  latter  has  been 
produced  at  excessive  temperatures.  The  percentage  of  fixed 
carbon  has  no  direct  significance  other  than  that  it  is  often  an 
identifying  characteristic.  This  is  particularly  true  of  grahamite, 
which  shows  from  40  to  50  per  cent.  The  Cuban  asphalt  is 
also  characteristically  high  in  fixed  carbon.  It  should  be  noticed 
that  the  Cuban  asphalt  carries  more  sulphur  than  any  of  the 
others. 

Asphaltic  Cements.  —  In  order  that  they  may  be  employed  in 
street  paving  it  is  necessary  that  the  solid  native  bitumens  be 
cut  or  fluxed  with  an  oily  body  until  sufficiently  soft  when 
heated  to  be  incorporated  with  the  mineral  aggregate  and  to 
produce  with  this  aggregate  a  mixture  which  while  having 
sufficient  rigidity,  when  laid,  to  withstand  displacement  under 
traffic,  will  not  be  so  hard  and  brittle  as  to  crack  under  service 
conditions.  Such  a  combination  of  asphalt  and  oil  produces  an 
asphaltic  cement. 

An  asphaltic  cement  for  paving  work  should  be  prepared  with 
a  flux  which  is  both  chemically  and  physically  stable  in  order 
that  it  may  not  be  subject  to  marked  permanent  changes  during 
or  after  application.  The  solid  bitumen  itself  is  relied  upon  to 
give  the  cement  its  binding  properties  and  the  flux  acts  mainly 
as  a  softening  agent.  Petroleum  residuums  have  been  almost 
exclusively  used  for  this  purpose,  and  many  of  these  residuums, 
which  by  themselves  would  prove  absolutely  unfit  for  any  sort 
of  road  treatment,  are  well  adapted  for  the  preparation  of  as- 
phaltic cements.  Thus  the  paraffin  residuums  when  not  too 
rich  in  paraffin  scale  have  been  successfully  utilized  as  fluxes 
for  the  asphalts.  Residuums  which  will  harden  after  applica- 
tion, while  in  themselves  suited  for  road  treatment,  will  not 
prove  satisfactory  as  fluxes  in  the  preparation  of  ordinary 
asphaltic  cements  as  the  cement  itself  will  then  rapidly  become 
too  brittle  after  being  mixed  with  the  mineral  aggregate.  Speci- 


SEMISOLID    AND    SOLID    NATIVE   BITUMENS  1 93 

fications  for  fluxes  usually  require  that  when  heated  for  seven 
hours  at325°F.  (i63°C.)  the  flux  shall  not  volatilize  more  than 
5  per  cent  of  oil  and  that  it  shall  be  soluble  in  88  degrees  naphtha 
to  not  less  than  90  per  cent.  The  latter  clause  is  inserted  in 
order  that  the  so-called  malthenes  and  asphaltenes  may  be  kept 
in  normal  proportions,  without  the  use  of  an  excessive  amount 
of  the  flux. 

In  the  preparation  of  road  binders  from  the  solid  native 
bitumens,  the  same  kind  of  flux  employed  in  the  paving  industry 
should  be  used  when  it  is  desired  to  secure  a  binder  whose  normal 
consistency  is  to  be  maintained  after  application.  A  greater 
amount  of  the  flux  can,  however,  be  employed  in  the  preparation 
of  these  binders  as  it  is  possible  to  employ  a  much  softer  as- 
phaltic  cement  with  a  coarse  mineral  aggregate,  such  as  occurs 
in  a  road,  than  with  the  sand  aggregate  of  the  sheet  asphalt 
pavement. 

In  some  instances  it  is  desirable  to  make  use  of  a  binder  of 
softer  consistency  than  should  be  permanently  maintained,  in 
order  that  it  may  be  applied  easily.  When  this  is  the  case  a 
partially  volatile  or  self-hardening  flux  should  be  employed 
which  will  cause  the  binder  to  become  harder  after  application. 
Such  asphaltic  cements  are  quite  comparable  with  the  cut  back 
oil  products  mentioned  in  the  preceding  chapter. 

Asphaltic  cements  employed  in  the  paving  industry  are  pre- 
pared as  follows:  A  weighed  quantity  of  the  solid  bitumen  is 
melted  in  a  suitable  tank  and  brought  to  a  temperature  of 
about  163°  C.  A  predetermined  proportion  of  flux  which  has 
by  trial  been  found  to  produce  a  cement  of  the  desired  consist- 
ency is  then  run  into  the  melted  bitumen.  The  flux  is  pre- 
viously heated  to  about  95°  C.  and  is  added  slowly,  the  mixture 
being  meanwhile  agitated  by  a  current  of  air  or  dry  steam. 
Agitation  is  continued  until  the  solid  bitumen  and  flux  are 
thoroughly  incorporated,  from  three  to  eight  hours  being  ordi- 
narily sufficient  to  accomplish  this.  As  a  rule  steam  agitation 
is  to  be  preferred  to  air  as  the  latter  is  apt  to  cause  chemical 
changes  in  the  cement,  of  the  same  character  as  described  under 


194  DUST   PREVENTIVES  AND    ROAD   BINDERS 

blown  oils,  and  such  changes  are  likely  to  produce  a  material 
lacking  in  uniformity  unless  its  consistency  is  carefully  watched 
and  controlled  by  determinations  made  from  time  to  time.  If 
steam  is  employed,  care  should  be  taken  to  prevent  its  partial 
condensation  before  being  forced  through  the  mixture  or  other- 
wise the  water  carried  along  will  cause  the  cement  to  foam 
badly.  Any  water  present  in  the  flux  will  have  the  same  effect 
and  it  is,  therefore,  customary  to  specify  that  the  flux  must  be 
free  from  water. 

Mechanical  agitation  is  sometimes  resorted  to  and  serves  the 
same  purpose  as  steam  or  air  agitation,  although  perhaps  not 
quite  so  effectively.  Besides  being  necessary  for  a  thorough 
mixing  of  flux  and  solid  bitumen,  agitation  prevents  local  over- 
heating to  a  great  extent  and,  therefore,  cracking  and  coking 
of  the  heavier  hydrocarbons. 

Sometimes  blown  oils  are  employed  as  fluxes  for  compara- 
tively small  amounts  of  the  solid  native  bitumens.  Such 
mixtures  containing  gilsonite  have  been  quite  extensively 
manufactured  in  the  past  few  years  and  sold  both  for  street 
paving  and  road  work.  The  gilsonite  is  crushed  fine  and  added 
directly  to  the  flux  while  still  in  the  converter.  The  flux  is 
partially  blown  before  the  addition  is  made  and  is  maintained 
at  a  temperature  of  about  205°  C.  After  the  gilsonite  has  been 
added,  the  blowing  process  is  continued  until  the  cement  attains 
the  desired  consistency.  Refined  tars  or  tar  residuums  in  con- 
junction with  oil  residuums  have  also  been  employed  as  fluxes 
for  gilsonite  in  the  preparation  of  road  binders.  The  gilson- 
ite cements  are  as  a  rule  short  and  non-ductile,  but  possess  a 
rubbery  consistency  quite  different  from  the  true  asphalt 
cements.  Blown  oil  gilsonite  products  have  been  sold  under 
the  name  of  mineral  rubber  and  the  pavements  in  which  they 
have  been  employed  are  known  as  mineral  rubber  pavements. 
The  characteristics  of  a  typical  blown  oil  gilsonite  cement  are 
given  in  the  following  table. 


SEMISOLID   AND    SOLID   NATIVE   BITUMENS  1 9$ 

BLOWN    OIL    GILSONITE    CEMENT. 

Character Short  but  sticky 

Specific  gravity,  25°/25°  C °-979 

Melting  point,  degrees  C 75° 

Penetration  25°  C.,  No.  2  N.,  100  gms.,  5  sec 32° 

Loss  at  i63°C.,  5  hours 0.57% 

Character  of  residue somewhat  harder 

Penetration  of  residue  (as  above) 21° 

Soluble  in  CS2,  air  temperature 99 . 57% 

Organic  material  insoluble .  29% 

Inorganic  material .14% 

100.00 

Per  cent  bitumen  insoluble  in  86°  naphtha,  air  temp 26.00% 

Fixed  carbon 9 . 36% 

When  tar  is  employed  as  a  flux  for  gilsonite,  it  has  been  cus- 
tomary to  first  prepare  a  gilsonite  oil  cement  of  about  the  con- 
sistency of  an  ordinary  asphalt  cement  and  then  to  cut  this 
product  with  a  fluid  tar  residuum  until  the  mixture  has  at- 
tained the  consistency  of  a  very  viscous  liquid.  The  proper- 
ties of  such  a  mixture  prepared  for  use  as  a  permanent  road 
binder  are  given  below. 

GILSONITE    OIL    TAR    PREPARATION. 

Specific  gravity,  25°/25°  C i .  127 

Character Viscous,  sticky 

Loss  at  100°  C.,  5  hours i .  35% 

Loss  at  163°  C.,  7  hours 1 1 . 74% 

Loss  at  205°  C.,  7  hours 19 . 36% 

Character  of  residue Cracked,  brittle 

Distillation  Test: 

Distillate  to  no0  C.,  per  cent  by  volume Trace 

*Distillate  no0  to  170°  C.,  per  cent  by  volume 4-9% 

fDistillate  170°  to  240°  C.,  per  cent  by  volume 26.3% 

Pitch  residue 68  .8% 

100.  O 

Soluble  in  CS2,  air  temperature 96. 62 

Organic  matter  insoluble 3 . 18 

Inorganic  matter .20 

100.00 

Insoluble  in  CC14,  air  temperature 8. 61% 

Insoluble  in  90  per  cent  benzol,  air  temperature 6.21 

*  This  distillate  when  cold  held  about  one-twelfth  its  volume  precipitated  solids, 
f  This  distillate  when  cold  held  only  a  very  small  amount  of  solids.     It  separated 
into  two  layers,  one  apparently  an  oil  and  the  other  a  tar  product. 


196  DUST   PREVENTIVES    AND    ROAD    BINDERS 

An  asphaltic  cement  for  street  paving  should  in  most  cases 
show  a  penetration  at  25°  C.  of  between  30  and  90.  The  de- 
sired consistency,  as  has  been  stated,  is  obtained  by  using  the 
proper  amount  of  flux.  The  proportion  of  solid  bitumen  to  flux 
must  of  necessity  vary  with  the  character  of  both.  Thus  an 
extremely  hard  asphalt  will  ordinarily  require  more  flux  than  a 
comparatively  soft  one  and  a  greater  amount  of  a  dense  resid- 
uum will  be  required  than  of  a  more  fluid  one  in  order  to 
produce  a  cement  of  a  given  consistency.  No  definite  rule  can 
however  be  laid  down  in  regard  to  this  matter.  The  percentage 
of  naphtha  insoluble  bitumen  in  a  normal  cement  will  usually 
lie  between  20  and  35  per  cent.  For  street  paving  work  such 
properties  as  susceptibility  to  temperature  changes,  stability 
and  ductility  are  important  points  to  be  considered.  For  road 
treatment  much  broader  limits  may  be  allowed,  and  while  it 
may  sometimes  be  desirable  to  employ  a  road  binder  having  a 
penetration  of  200  or  less,  good  results  may  often  be  obtained 
by  the  use  of  viscous  fluid  bitumens  originally  too  soft  for  a 
penetration  determination,  but  which  will  in  time  attain  a  con- 
siderably harder  consistency.  Except  when  blown  oil  products 
are  employed  it  is  probably  desirable  that  the  cement  show  a 
higher  penetration  than  in  sheet  asphalt  work  for  the  reason 
that  in  road  work  the  binder  is  not  depended  upon  to  produce 
stability  in  the  mineral  aggregate,  and  the  softer  binders  are 
not  so  apt  to  become  brittle  at  low  temperatures. 

Summary  and  Conclusions.  —  In  this  chapter  the  physical 
and  chemical  characteristics  of  the  semisolid  and  solid  native 
bitumens  have  been  considered  with  especial  reference  to  their 
use  as  road  binders.  No  attempt  has  been  made  to  discuss 
their  relative  merits  as  applied  to  sheet  asphalt  pavements, 
other  than  to  show  the  most  important  differences  which  exist 
between  the  two  subjects.  The  asphalt  pavement  has  been 
very  exhaustively  treated  by  Richardson  to  whose  work  *  the 
reader  is  referred  for  further  information  along  this  line. 

One  of  the  most  important  facts  which  should  be  noted  is 

*  "  The  Modern  Asphalt  Pavement,"  Wiley  and  Sons. 


SEMISOLID    AND   SOLID   NATIVE   BITUMENS  197 

that  binders  totally  unsuited  for  the  construction  of  sheet 
asphalt  surfaces  may  often  have  very  desirable  qualities  for 
use  as  road  binders.  While  the  data  accumulated  in  the  pav- 
ing industry  relative  to  the  characteristics  of  various  solid  bitu- 
mens and  fluxes  are  well  worthy  of  careful  study,  the  standards 
so  developed  can  by  no  means  be  considered  a  criterion  for  road 
work,  and  this  is  a  point  which  should  be  remembered  but  which 
is  often  overlooked. 

Nearly  all  of  the  bitumens  described  in  this  chapter  are  suit- 
able or  can  be  made  suitable  for  various  types  of  road  work,  but 
owing  to  cost  it  is  doubtful  if  many  of  them  will  ever  be  exten- 
sively employed  for  this  purpose.  The  domestic  products  such 
as  the  malthas,  rock  asphalts  and  gilsonite  will  of  course  be 
employed  to  some  extent,  especially  in  localities  in  which  they 
occur.  It  is  doubtful,  however,  if  the  more  costly  imported 
asphalts  will  be  able  to  successfully  compete  with  the  cheaper 
artificial  asphalts  which  are  now  produced  in  large  quantities 
for  road  work  and  which  if  properly  prepared  should  give  excel- 
lent service. 


CHAPTER  X. 

THE  APPLICATION   OF   PETROLEUM  AND   ASPHALTIC 
MATERIALS. 

IN  this  country  the  first  attempt  to  treat  road  surfaces  with 
petroleum  was  made  in  Santa  Barbara  County,  California,  in 
1894.  Crude  petroleum  from  the  Summerland  wells  was  sprin- 
kled upon  an  earth  road  for  the  purpose  of  laying  the  dust.  It 
proved  very  effective  as  a  dust  preventive,  and  being  asphaltic 
in  character  improved  the  condition  of  the  road  surface  to  such 
an  extent  that  popular  attention  was  aroused,  and,  as  a  result, 
many  experiments  were  commenced  with  a  view  not  only  to 
laying  the  dust  but  to  bonding  the  surface  as  well.  By  1898 
the  use  of  crude  California  oil  for  road  treatment  had  spread 
through  a  number  of  counties,  where  it  had  come  to  be  gener- 
ally regarded  as  the  solution  of  the  dust  problem,  especially  by 
fruit  growers  whose  industry  had  long  been  injured  by  the 
damaging  effect  of  road  dust  upon  their  produce.  By  1899  the 
treatment  of  roads  with  both  crude  and  residual  oils  had  ex- 
tended to  a  number  of  other  states,  and  by  1902  experiments 
had  been  reported  from  Texas,  Pennsylvania,  New  Jersey,  In- 
diana, Colorado  and  the  District  of  Columbia.  By  1904  the 
field  had  broadened  still  further,  but  the  work  had  all  been  of 
an  experimental  nature  and  the  most  varying  results  were  re- 
ported. The  only  important  fact  that  had  been  generally 
learned  as  to  the  relative  value  of  different  petroleums  was  that 
the  paraffin  oils  had  not  proved  satisfactory  for  road  treatment 
and  that  those  of  an  asphaltic  nature  were  to  be  preferred.  In 
California,  where  work  was  naturally  confined  to  this  type  of 
oil,  good,  bad  and  indifferent  results  had  been  obtained  so  far 
as  improvement  of  the  road  surface  was  concerned,  although 
from  the  standpoint  of  dust  suppression  the  work  had  proved 

198 


APPLICATION   OF   PETROLEUM   AND    ASPHALT  199 

very  successful.  Road  engineers  had  begun  to  realize  that  in 
order  to  produce  good  results  something  more  was  necessary 
than  to  pour  any  kind  of  oil  upon  any  kind  of  road  surface.  Oil 
sprinklers  or  wagons  fitted  with  spreading  devices  had  become 
quite  common,  and  the  use  of  the  heavier  crude  and  residual 
oils  which  required  heating  before  they  could  be  successfully 
applied,  was  regarded  as  best  practice. 

In  1905  the  use  of  oil  for  road  treatment  advanced  rapidly  and 
during  the  last  four  years,  owing  to  the  very  widespread  interest 
in  the  problems  of  dust  suppression  and  road  preservation,  the 
total  mileage  of  oil  treated  roads  has  increased  by  leaps  and 
bounds.  Road  oil  industries  have  been  developed  for  the  pur- 
pose of  producing  and  selling  oils  suitable  for  application  in  a 
variety  of  ways  under  varying  conditions.  These  products  have 
been  used  indiscriminately  and  the  greatest  variations  in  re- 
sults have  been  reported.  The  whole  subject  is  yet  in  an  ex- 
perimental stage  and  much  is  to  be  learned  as  to  the  effect  of 
certain  physical  and  chemical  properties  of  an  oil  upon  the 
results  obtained  in  practice.  Unfortunately  the  consumer  while 
responsible  for  numerous  experiments  has  as  a  rule  neglected  to 
make  an  examination  of  the  oil  he  has  employed,  and  this  fact 
has  to  a  great  extent  detracted  from  the  value  of  his  reports 
for  others  who  wish  to  work  along  similar  lines.  While  some 
attempts  have  been  made  to  review  these  reports,  the  conclu- 
sions arrived  at  by  this  means  are  vague  at  best,  and  road  en- 
gineers are  often  forced  to  learn  by  experience  what  should  by 
this  time  be  common  knowledge. 

California  is  particularly  favored  by  nature  for  oil  road  work, 
as  regards  the  character  of  her  oils,  her  climate  and  her  soil. 
Experimenters  in  other  states  have  not  as  a  rule  realized  the 
importance  of  this  fact,  .and  in  attempting  to  duplicate  Cali- 
fornia methods  have  met  with  failure  because  of  different  local 
conditions  which  require  somewhat  different  treatment. 

Application  of  Oils  in  General.  —  The  subject  of  oil  applica- 
tion, unlike  that  of  tar,  has  received  considerably  more  study 
in  this  country  than  has  been  given  it  by  European  nations.  It 


200  DUST   PREVENTIVES   AND   ROAD   BINDERS 

is  true  that  various  experiments  have  been  carried  on  in  England 
and  France  with  a  number  of  different  oils,  but  owing  to  the 
lack  of  a  proper  base  in  these  oils  the  results  have  been  dis- 
couraging. Shale  oils  and  Russian  petroleum  residuums,  known 
as  "masut"  or  "astatki,"  have  been  employed.  They  have  all 
been  found  effective  as  temporary  dust  preventives,  but  in 
rainy  weather  produce  a  greasy,  disagreeable  mud  and  soon 
disappear  from  the  road  surface.  The  best  results  have  so  far 
been  obtained  with  heavy  oils  applied  in  the  form  of  a  spray 
while  hot. 

Under  favorable  conditions  oils  may  be  applied  to  earth, 
gravel  and  broken  stone  roads  with  good  results,  and  in  any 
case  application  may  be  made  either  to  the  surface  of  an  old 
road  or  to  the  body  of  the  road  during  resurfacing  or  construc- 
tion. In  broken  stone  roads  the  roads  tone  may  also  be  mixed 
with  the  oil  before  being  laid,  in  which  case  the  work  more  nearly 
resembles  the  city  street  form  of  construction.  A  number  of 
distributing  devices  have  been  invented  for  the  purpose  of  facil- 
itating application,  and  special  machinery  has  been  designed  for 
convenient  handling  and  transportation  of  the  oil  as  well  as  for 
incorporating  it  with  the  road  material. 

Surface  Application  of  the  Lighter  Crude  Oils.  —  An  oil  ap- 
plied to  the  surface  of  a  road  will  serve  only  as  a  temporary  or 
semipermanent  binder.  Crude  oils  with  the  exception  of  those 
found  in  California  should  be  considered  mainly  as  dust  pre- 
ventives as  they  have  little  to  recommend  them  as  road  bind- 
ers. If  sufficiently  fluid  they  may  be  applied  cold  by  means  of 
an  ordinary  street  sprinkler,  but  only  in  sufficient  quantity  to 
saturate  the  dust  present  on  the  road.  A  number  of  light 
applications  during  a  dusty  season  is  to  be  greatly  preferred  to 
a  single  heavy  one,  for  the  latter  is  apt  to  be  incompletely 
absorbed  by  the  road  and  will  require  sanding  in  order  to  take 
up  all  excess  of  oil.  Even  then  the  surface  will  become  greasy 
and  slippery  unless  the  oil  is  very  asphaltic  in  character. 
In  addition  the  road  will  cut  up  badly  under  traffic  in  wet 
weather. 


APPLICATION    OF  PETROLEUM   AND   ASPHALT  2OI 

No  set  rule  can  be  laid  down  as  to  the  proper  quantity  to 
apply  because  of  the  variance  in  the  capacity  for  absorption 
of  different  road  surfaces.  Earth  roads  will  require  more  than 
gravel  roads  and  gravel  roads  more  than  macadam.  The  con- 
sistency of  the  oil  itself  may  often  modify  the  amount  required 
as  the  very  fluid  oils  will  be  absorbed  more  readily  than  those 
which  are  non-viscous.  The  ideal  treatment  would  be  to  use 
just  sufficient  oil  at  one  application  to  lay  the  dust  for  a  season 
and  at  the  same  time  prevent  the  formation  of  an  undesirable 
surface  condition.  This  is  of  course  a  difficult  matter  to  esti- 
mate, but  for  macadam  roads  will  average  from  0.3  to  0.6  gal- 
lons per  square  yard  and  for  earth  roads  sometimes  as  high  as 
1.5  gallons  and  over  per  square  yard.  Gravel  roads  will  re- 
quire an  intermediate  amount.  If  containing  a  relatively  large 
quantity  of  volatile  oils  the  crude  asphaltic  petroleums  may 
develop  considerable  binding  power  in  the  course  of  time  under 
atmospheric  conditions  and,  as  has  been  stated,  it  was  this  prop- 
erty that  first  aroused  public  attention  in  California. 

The  cost  of  treating  a  road  surface  with  crude  oil  can  be 
only  approximately  estimated,  as  the  value  of  the  oil  varies  in 
different  localities  (see  statistical  tables,  Chapter  VIII),  and 
the  amount  of  oil  required  is  an  uncertain  quantity.  In  gen- 
eral the  method  is  not  to  be  recommended  unless  the  oil  holds 
a  truly  asphaltic  base  and  the  dust  can  be  successfully  laid  for 
not  over  three  cents  per  square  yard  per  season. 

Application  of  Oil  Emulsions.  —  Emulsions  are  applied  to  the 
road  surface  in  much  the  same  manner  as  the  fluid  crude  oils, 
i.e.,  after  dilution  they  are  sprinkled  upon  the  road  by  means 
of  an  ordinary  street  sprinkler.  As  it  is  necessary  to  dilute  them 
before  using  a  method  similar  to  that  described  for  calcium 
chloride  (see  page  49)  by  which  they  may  first  be  distributed 
at  the  different  hydrants  along  the  road,  is  the  one  which  is 
most  apt  to  prove  economical.  The  quality  of  the  oil  con- 
tained in  the  emulsion  is  of  course  a  very  important  factor  to 
be  considered  and  only  those  holding  a  good  asphaltic  base 
should  be  used.  Preparations  of  this  sort  are  now  found  upon 


202  DUST   PREVENTIVES   AND    ROAD   BINDERS 

the  market  or  may  be  made  by  the  road  supervisor  as  described 
in  the  preceding  chapter. 

When  employing  the  class  of  asphaltic  oil  emulsions  now 
found  upon  the  market  it  is  customary  to  give  the  road  either  one 
treatment  or  else  two,  with  a  short  interval  between,  of  a  15  to 
1 8  per  cent  solution.  The  surface  is  thus  thoroughly  impreg- 
nated with  the  asphaltic  binder,  and  as  the  emulsifying  agents 
are  more  or  less  volatile,  an  insoluble  and  almost  waterproof 
deposit  is  finally  fprmed  upon  drying.  This  binder  is  not  easily 
removed  by  rains  or  traffic,  and  if  weaker  solutions  containing 
about  5  per  cent  of  the  original  emulsion  are  applied  from  time 
to  time  the  dust  will  be  well  laid.  At  the  end  of  a  season  the 
road  should  not  only  be  in  better  condition  than  at  the  beginning, 
but  its  wearing  quality  should  be  more  or  less  permanently 
improved,  according  to  the  amount  of  binder  which  has  been 
retained.  These  emulsions  can  be  purchased  for  about  sixteen 
cents  per  gallon  in  concentrated  form,  and  are  usually  contained 
in  iron  drums  holding  one  hundred  and  twenty  gallons  each.  In 
the  first  treatments  one  gallon  of  the  original  emulsion  is  applied 
to  about  every  thirty  square  yards,  and  for  succeeding  treat- 
ments the  same  amount  is  made  to  cover  from  sixty  to  ninety 
square  yards,  according  to  the  strength  of  solution  employed. 
The  total  cost  per  square  yard  during  an  average  season  will 
run  from  four  to  six  cents,  according  to  locality  and  traffic  con- 
ditions. While  this  is  somewhat  higher  than  the  cost  of  treating 
with  soap  emulsions  of  oil,  the  results  obtained  are  more  per- 
manent, and  this  fact  should  be  taken  into  account  when  com- 
paring the  two.  Up  to  the  present  time  the  oil  emulsions  have 
been  used  principally  upon  parkways  and  suburban  roads,  as 
the  cost  of  frequent  treatment  precludes  their  use  on  rural 
highways. 

When  intelligently  and  systematically  applied,  the  appear- 
ance of  a  macadam  road  so  treated  is  at  the  end  of  a  season 
much  improved  and  for  the  depth  of  from  one-quarter  to  one- 
half  inch  should  show  an  accumulation  of  asphaltic  oil  which 
binds  the  surface  stone  together  sufficiently  to  withstand  the 


APPLICATION    OF  PETROLEUM   AND   ASPHALT  2O3 

ordinary  disintegrating  effect  of  winter  weather.  At  the  begin- 
ning of  the  next  dusty  season,  however,  the  treatments  should 
be  renewed.  The  treatment  of  earth  roads  with  emulsions  is 
not  to  be  advised  because  of  the  high  cost  resulting  from  the 
necessarily  large  quantity  required.  It  is  possible  that  satis- 
factory results  may  be  obtained  at  a  reasonable  cost  in  the 
treatment  of  sand-clay,  burnt-clay  and  gravel  roads,  but  the 
macadam  certainly  offers  the  best  field  for  this  type  of  binder. 
Extremely  heavy  asphaltic  oil  emulsions  which  will  quickly 
evaporate  to  the  consistancy  of  a  semisolid  binder  have  been 
used  to  a  limited  extent,  in  the  neighborhood  of  Chicago,  in  the 
construction  of  macadam  roads.  Roads  so  built  have  not,  how- 
ever, been  down  for  a  sufficiently  long  time  to  warrant  any 
definite  opinion  as  to  their  merits. 

When  soap  emulsions  are  prepared  according  to  the  formula 
given  in  Chapter  VIII,  it  is  good  practice  to  apply  a  16  per  cent 
solution  at  first  and  from  5  to  10  per  cent  solutions  following, 
according  to  the  needs  of  the  road.  The  number  of  applications 
required  during  a  season  will  vary  with  conditions.  They  are 
usually  made,  however,  from  ten  to  twenty-five  days  apart. 
By  the  use  of  a  soap  emulsion  of  this  kind  the  loose  material 
on  the  road  is  held  down,  but  is  not  bound  firmly  together  nor 
to  the  road  surface.  A  thin  rolling  cushion  is  produced,  satu- 
rated with  oil,  which  prevents  dust  formation  and  protects  the 
underlying  surface.  A  very  light  coating  of  sand  or  fine  stone 
screenings  is  sometimes  spread  on  the  road  before  applying  the 
emulsion.  This  produces  a  surface  which  is  hard  and  firm  and 
will  take  a  considerable  amount  of  wear.  The  main  objection 
to  this  thin  rolling  cushion  is  that  under  the  action  of  traffic  it 
is  apt  to  be  worked  to  the  sides  of  the  road  and  finally  into  the 
gutters.  It  is  then  necessary  to  throw  the  old  material  back 
or  apply  fresh  material,  and  this  of  course  requires  constant 
attention  and  considerably  increases  the  cost  of  the  work.  In 
certain  cases  the  cost  of  applying  sufficient  emulsion  to  lay  the 
dust  for  a  season  has  been  as  low  as  two  cents  per  square  yard, 
as  compared  with  the  cost  of  watering  in  previous  seasons,  of 


204  DUST   PREVENTIVES    AND    ROAD   BINDERS 

three  cents  per  square  yard.  The  cost  of  applying  sand  and 
throwing  back  material  which  is  carried  to  the  gutters  should, 
however,  be  added  to  this  in  order  to  obtain  the  actual  cost  of 
maintaining  the  road  in  proper  condition.  Except  for  a  rather 
faint  oily  odor,  no  unpleasant  results  are  obtained  from  an 
emulsion  of  this  sort.  The  principal  advantage  is  its  cheapness, 
which  is  due  to  the  fact  that  it  is  manufactured  by  the  experi- 
menter. It  has  been  found  that  if  too  much  is  applied  at  one 
time  an  undesirable  loose  scale  is  formed  when  the  surface  dries 
out.  This  is  undoubtedly  due  to  the  soap  used,  which  to  some 
extent  destroys  the  true  binding  value  of  the  asphaltic  base, 
owing  to  the  presence  of  fixed  alkalies.  Light  applications  at 
more  frequent  intervals  are,  therefore,  to  be  preferred. 

Surface  Application  of  Heavy  Crude  and  Refined  Oils.  —  The 
heavy  crude  and  rather  viscous  residual  oils  and  cut  back  prod- 
ucts require  heating  before  they  can  be  applied  successfully  to  a 
road  surface.  Such  materials,  to  be  satisfactory,  should  serve 
as  semipermanent  binders,  as  the  cost  and  trouble  of  applying 
them  is  too  great  for  mere  dust  palliatives.  They  may  be  pur- 
chased by  the  barrel  or  by  the  tank  car,  the  latter  being  cheaper 
and  preferable  from  the  standpoint  of  heating,  provided  the  car 
is  properly  equipped  with  steam  coils. 

If  much  work  of  the  kind  is  to  be  carried  on  in  one  locality, 
it  is  sometimes  the  custom  to  erect  a  stationary  heating  plant 
at  a  convenient  railroad  siding.  A  plant  of  this  sort  may  con- 
sist of  a  receiving  tank  of  one  tank-car  capacity  placed  prefer- 
ably so  that  the  oil  may  be  run  in  by  gravity  from  the  car. 
A  heating  tank  set  at  an  elevation  sufficient  to  allow  the  hot 
oil  to  run  into  the  distributing  wagons,  and  fitted  with  steam 
coils  through  which  superheated  steam  may  be  forced,  is  placed 
near  the  receiving  tank.  The  oil  may  be  pumped  into  this 
heating  tank  as  required  and  heated  to  any  desired  temperature. 
Very  often  the  heating  is  carried  on  -in  the  tank  car,  and  the 
hot  oil  run  directly  into  the  distributing  wagon.  When  suffi- 
ciently fluid,  it  can  then  be  applied  to  the  road  by  means  of  a 
large  pipe  and  broomed  into  the  surface.  Patented  distribut- 


APPLICATION    OF   PETROLEUM   AND  ASPHALT  205 

ing  devices  have  been  employed  which  can  be  attached  to  almost 
any  form  of  tank  wagon  and  which,  if  the  oil  is  fluid  enough, 
will  do  away  with  the  necessity  of  brooming.  An  oil  applied 
by  this  means  will,  however,  have  to  be  heated  to  a  higher 
temperature  than  in  the  former  case,  as  the  openings  in  the 
distributer  are  of  small  dimensions  and  will  not  allow  the  oil  to 
pass  freely  if  it  is  in  a  very  viscous  state. 

Oil  Sprinklers.  —  Oil  sprinkling  carts  equipped  with  com- 
pressed air  chambers  for  the  purpose  of  forcing  the  hot  oil  upon 
the  road  in  a  fine  spray  under  pressure  are  now  being  used  to 
some  extent  and  are  to  be  recommended,  for  by  this  means  a 
uniform  distribution  can  be  secured  and  the  quantity  of  oil 
applied  per  given  area  easily  controlled.  Such  a  machine  is 


FIG.  15.     Saybolt  High  Pressure  Road  Oil  Distributor. 

shown  in  Fig.  15,  and  types  of  oil  distributing  devices  which 
may  be  attached  to  the  ordinary  sprinkler  in  Figs.  16,  17  and  18. 
Fig.  15  shows  a  lately  devised  high-pressure  automatically  pro- 
pelled road  oiler  of  an  American  make.     This  machine  deserves 


206 


DUST   PREVENTIVES    AND    ROAD   BINDERS 


notice  as  being  one  of  the  first  of  its  kind  manufactured  in  the 
United  States,  although  somewhat  similar  machines  have  been 
used  in  England  and  France  for  some  time  past  and  a  few 
imported  to  this  country.  During  the  summer  of  1909  it  was 
tried  out  in  practice  in  a  number  of  the  eastern  states  with 
considerable  success. 


FIG.  16.     Asphaltoilene  Distributor. 

In  Fig.  1 6,  A  A  represent  the  conveyors  which  carry  the  oil 
from  the  tank  wagon  to  the  distributor,  and  BBBB  levers  oper- 
ating the  four  valves  which  control  the  flow  of  oil  from  the 
four  sections  of  the  distributor  E,  which  is  six  feet  wide.  Each 
lever  is  provided  with  a  ratchet  and  can  be  adjusted  to  deliver 
from  one  pint  to  two  gallons  to  the  square  yard  for  a  width  of 
eighteen  inches.  The  lever  D  serves  as  a  foot  rest  for  the  oper- 
ator, who  sits  in  the  seat  F  and  operates  a  valve  for  rapid 
control  of  the  entire  flow.  The  distributor  is  attached  to  the 
sprinkling  wagon  by  means  of  supports  GGGG  which  are  braced 


APPLICATION  OF  PETROLEUM  AND    ASPHALT  2O/ 

by  the  attachments  HH.     Fig.   17  shows  this  distributor  in 
operation. 


FIG.  17.     Asphaltoilene  Distributor  in  Operation. 

Fig.   1 8  shows  another  type  of  detachable  distributor  con- 
sisting of  an  equalizing  tank  or  reservoir  connected  with  the 


FIG.  18.    American  Tar  Company's  Distributor. 


208  DUST   PREVENTIVES   AND    ROAD   BINDERS 

distributing  pipe  and  mounted  on  wheels.  It  may  be  readily 
attached  to  any  kind  of  tank  wagon  fitted  with  an  outlet  pipe 
in  the  rear  as  there  are  no  complicated  connections,  the  dis- 
tributor being  simply  trundled  along  behind  the  wagon.  It  is 
operated  by  means  of  a  single  lever  and  is  so  arranged  that  it 
distributes  the  material  over  the  road  surface  to  any  width 
from  six  feet  to  six  inches.  Owing  to  the  equalizing  tank  a 
uniform  pressure  is  kept  on  the  distributing  nozzles  indepen- 
dent of  the  amount  of  liquid  in  the  tank  wagon. 

Measurement  of  Hot  Oils.  —  When  heating  an  oil  for  appli- 
cation it  is  advisable  to  raise  its  temperature  only  just  high 
enough  to  allow  to  be  easily  handled  and  properly  applied.  The 
minimum  temperature  will  necessarily  vary  with  different  oils 
according  to  their  composition  and  original  viscosity,  but  in  no 
case  should  an  oil  or  oil  product  be  heated  higher  than  350°  F. 
(177°  C.).  It  is  sometimes  desirable  to  measure  this  oil  while 
hot  and  for  this  purpose  its  volume  at  60°  F.  (15.5°  C.)  is  taken 
as  normal  and  a  deduction  of  0.4  per  cent  is  made  for  every 
10°  F.  increase  over  the  normal  temperature,  as  a  correction 
for  expansion  by  heat.  Thus  if  a  tank  wagon  having  a  capacity 
of  six  hundred  gallons  is  filled  with  oil  at  a  temperature  of 
260°  F.  the  actual  amount  of  oil  at  60°  F.  would  be  calculated 
as  follows: 

600  -T-  ( X  .004  +  i  )=  555.5  gals. 

\       10  / 

The  general  formulas  for  finding  the  volume  of  a  hot  oil  at  nor- 
mal temperature,  calculated  by  means  of  Fahrenheit  and  Centi- 
grade degrees  are  given  below,  V  being  in  both  cases  the  volume 
while  hot. 

Volume  at  60°  F.  = V  • 

.0004  (  F.  -  60)  +  i 

Volume  at  15. 5°  C. 


.00072  (°C.-i5.5)  +  i 

While  this  method  of  calculating  the  actual  volume  of  oil  is 
not  theoretically  correct,' owing  to  the  differences  in  coefficient 


APPLICATION   OF  PETROLEUM   AND  ASPHALT  2Og 

of  expansion  of  different  oils,  it  is  near  enough  for  all  practical 
purposes  and  is  customarily  used  for  asphaltic  oils.  It  is,  how- 
ever, preferable  to  purchase  oil  by  weight  if  it  is  delivered  hot 
and  the  facilities  for  weighing  it  are  at  hand. 

Surface  Treatment  of  Earth  Roads.  —  The  surface  treat- 
ment of  earth  roads  with  heavy  oils  is  now  almost  a  thing  of 
the  past,  as  it  has  been  found  far  more  satisfactory  to  harrow 
the  oil  into  the  body  of  the  road  and  practically  construct  an 
oil-earth  road.  If  a  purely  surface  application  is  to  be  made 
with  an  asphaltic  oil,  the  surface  may  be  improved  to  some 
extent  by  the  formation  of  a  thin  crust  of  oiled  earth,  which 
will,  however,  tend  to  break  through  and  scale  off.  If  a  semi- 
asphaltic  oil  is  used,  the  surface  will  become  mealy,  and  while 
the  dust  may  be  laid  for  some  time,  a  disagreeable  mud  will  be 
formed  in  wet  weather.  Before  application  the  road  should 
be  shaped  up  with  a  drag  or  road  machine,  all  loose  places  com- 
pacted and  ruts  well  filled,  as  the  oil  tends  to  collect  in  the  low 
places  and  unless  well  mixed  with  the  earth  will  form  soft 
spots.  The  surface  should  not  be  rolled  to  any  extent  as  it  is 
desirable  to  have  about  one-half  inch  of  loose  earth  to  absorb 
the  oil.  After  application  this  cushion  of  oiled  earth  should 
compact  sufficiently  under  traffic. 

It  has  been  found  that  the  character  of  the  soil  plays  a  most 
important  part  in  the  results  obtained,  and  different  kinds  of 
soils  have  to  be  treated  in  different  ways.  Alkali  soils  disinte- 
grate the  oil  and  destroy  its  binding  qualities.  A  sandy  loam 
is  the  most  suitable  for  treatment,  and  almost  invariably  gives 
good  results  when  treated  in  the  proper  manner  with  an  oil  of 
good  binding  quality.  From  a  physical  standpoint  clay  is 
probably  the  worst  of  all,  as  it  does  not  absorb  the  oil  well  and 
exhibits  a  tendency  to  ball  up  and  give  trouble.  Sand  should 
therefore  be  added  to  the  clayey  surface  until  this  difficulty  is 
overcome.  Special  attention  should  be  paid  to  drainage,  and 
the  roadbed  should  be  dry  when  the  oil  is  applied.  If  the 
foundation  is  water-soaked,  it  soon  loses  its  ability  to  properly 
support  the  surface,  which  will  then  break  through  in  weak 


210  DUST   PREVENTIVES    AND    ROAD    BINDERS 

spots.  The  use  of  too  much  oil  should  be  avoided,  as  it  will 
produce  a  spongy  surface  condition  and  increase  the  draft  of 
vehicles  to  a  considerable  extent. 

Surface  Treatment  of  Gravel  Roads.  —  Gravel  roads  are  as  a 
class  better  adapted  to  surface  treatment  with  heavy  oils  than 
any  other  and  in  the  eastern  part  of  the  United  States  have 
proven  most  satisfactory  when  the  proper  kind  of  oil  has  been 
employed.  In  fact  a  well  compacted  gravel  road  if  built  of  a 
good  cementing  gravel  requires  but  little  additional  binding 
material  to  lay  the  dust  and  put  it  in  condition  to  success- 
fully withstand  automobile  and  light  horse  drawn  traffic.  The 
application  of  even  a  temporary  binder  will  sometimes  produce 
surprisingly  satisfactory  results.  The  best  gravel  for  treatment 
with  oils  is  one  containing  just  sufficient  clayey  material  to  act 
as  a  natural  binder  for  the  larger  particles.  It  is  impossible  to 
state  just  the  proper  amount  of  clay  as  the  proportion  will  vary 
for  different  gravels.  Experiment  alone  will  determine  this  but 
it  will  be  found  that  too  much  clay  is  less  desirable  than  too 
little. 

It  is  very  important  in  a  gravel  road  that  the  drainage  be 
good,  and  this  matter  should  be  attended  to  first  of  all.  Any 
holes  or  pockets  which  may  exist  should  be  cleaned  out,  if  much 
fine  material  is  present,  and  filled  with  clean,  fresh  gravel,  so 
that  the  surface  of  the  road  will  be  uniform  when  the  patches 
have  been  sprinkled  and  rolled.  If  the  lateral  drainage  is  bad, 
the  entire  surface  should  be  loosened  and  brought  to  proper 
grade  and  crown  by  the  addition  of  new  material  before  the  oil  is 
applied.  In  this  case  more  oil  will  be  required  to  produce  a  good 
bond  than  if  the  old  compacted  surface  is  treated,  but  the  results 
will  be  of  a  more  lasting  character.  The  oil  should  contain  a 
high  percentage  of  good  asphaltic  base,  or  otherwise  the  material 
near  the  surface  will  become  loose,  owing  to  the  lubricating 
qualities  of  the  oil.  The  use  of  too  much  oil  should  be  especially 
avoided,  and  all  excess  should  be  taken  up  by  the  addition  of 
fresh  gravel.  Where  the  surface  treated  is  loose  and  contains 
a  considerable  amount  of  clay,  the  oil  may  be  worked  into  the 


APPLICATION   OF   PETROLEUM   AND    ASPHALT  211 

upper  course  by  raking,  which  insures  an  equal  distribution. 
After  application  of  the  oil,  the  road  should  be  rolled  until 
properly  compacted,  and  as  this  is  apt  to  bring  some  of  the  oil 
to  the  surface,  fresh  material  should  be  added  where  necessary. 
If  the  freshly  oiled  road  is  not  well  rolled,  the  action  of  traffic 
will  bring  the  oil  upward;  a  soft  spongy  surface  condition  will 
be  produced;  loose,  oily  particles  will  be  thrown  out  by  rapidly 
moving  vehicles;  and  the  oil  will  be  tracked  by  pedestrians. 

Shell  roads  may  be  treated  in  the  same  manner  as  described 
for  gravel  roads. 

Surface  Treatment  of  Macadam  Roads.  —  Before  applying 
a  semipermanent  oil  binder  to  a  macadam  surface,  it  is  abso- 
lutely essential  that  the  road  be  put  in  good  repair,  if  satis- 
factory results  are  to  be  obtained.  Failure  to  do  this  has 
resulted  in  many  unsuccessful  experiments  which  might  other- 
wise have  proved  entirely  satisfactory.  No  mere  surface 
application  will  ever  put  a  poor  road  in  good  condition,  and  the 
most  that  can  be  expected  from  an  oil  so  applied  is  that  it  shall 
keep  a  good  road  in  good  condition  for  a  reasonable  length  of 
time.  Much  of  course  depends  upon  the  character  of  the  oil, 
but  the  best  cannot  do  more  than  this.  Particular  attention 
should  be  paid  to  drainage  and  all  holes  and  depressions  should 
be  filled  and  the  surface  brought  to  even  crown  and  grade, 
sometime  in  advance  of  treatment,  in  order  that  the  repairs  may 
become  well  consolidated  by  traffic.  This  is  necessary  because 
most  oils  intended  for  the  surface  treatment  of  old  roads  have  not 
sufficient  binding  strength  to  hold  down  fresh  patches.  If 
applied  to  such  places  at  the  same  rate  as  to  the  rest  of  the 
road  they  are  apt  to  be  entirely  absorbed  into  the  body  of  the 
road,  and  if  in  larger  quantities  to  produce  soft  spots.  When  it 
is  impracticable  or  inconvenient  to  make  repairs  in  advance, 
the  use  of  some  heavier  binder  such  as  might  be  employed  in 
construction  work  is  to  be  advised  in  places  where  new  stone  is 
required. 

Before  applying  the  oil,  much  more  dust  may  be  allowed  to 
remain  upon  the  road  surface  without  bad  effect  than  in  the  case 


212  DUST   PREVENTIVES    AND    ROAD    BINDERS 

of  tars.  There  is  a  limit,  however,  which  is  often  exceeded  and 
this  has  been  the  cause  of  many  failures  in  oil  treated  roads. 
It  is  safe  to  say  that  a  very  dusty  road  should  always  be  swept 
before  oiling,  and  if  any  doubt  exists  as  to  the  advisability  of 
sweeping  the  road,  the  behavior  of  the  oil  itself  when  applied 
upon  a  short  section  should  serve  as  a  guide.  Other  things 
being  equal,  heavy  oils  should  produce  more  lasting  results 
than  light  oils,  but  owing  to  their  lower  penetrating  value,  they 
cannot  be  satisfactorily  applied  to  as  dusty  a  surface  as  the  latter. 
If,  therefore,  the  oil  tends  to  puddle  without  being  absorbed  by 
the  road  surface,  the  presence  of  too  much  dust  is  indicated. 
The  remainder  of  the  road  should  then  be  swept,  after  which  a 
better  absorption  or  penetration  of  the  oil  will  be  obtained. 
Under  the  conditions  mentioned  it  is  exceedingly  bad  practice 
to  continue  the  application  of  oil  to  the  dusty  surface  and  rely 
upon  a  coat  of  sand  or  screenings  to  hold  it  in  place,  and  yet 
this  is  often  done.  The  application  of  too  much  oil  is  also  a 
frequent  cause  of  failure.  All  macadam  surfaces  will  not  require 
the  same  amount,  and  as  no  set  rules  can  be  laid  down  in  this 
regard  it  is  a  matter  for  the  exercise  of  some  little  judgment. 
Too  often  application  is  made  by  rule  of  thumb  and  a  given 
quantity  of  oil,  usually  0.5  gallon  per  square  yard,  is  applied 
whether  or  no.  In  some  instances  0.3  gallon  is  more  than 
sufficient  and  in  others  0.6  or  0.7  gallon  per  square  yard  should 
be  applied,  depending  not  only  upon  the  condition  of  the  road 
surface  but  upon  the  character  of  the  oil  itself. 

The  condition  of  the  road  surface  with  respect  to  its  moisture 
contents  at  the  time  application  is  made  often  exerts  a  very 
marked  influence  upon  the  results  obtained.  This  matter 
requires  more  study  before  any  very  definite  assertions  can  be 
made,  but  it  may  be  said  that  while  an  oil  should  never  be 
applied  in  rainy  weather  or  to  an  absolutely  wet  surface,  a  slight 
amount  of  moisture  is  preferable  to  an  absolutely  dry  and  pow- 
dery surface.  Instances  have  come  under  the  writer's  notice 
where  sections  of  the  same  road  built  of  the  same  rock  and 
apparently  in  the  same  condition,  have  produced  somewhat 


APPLICATION    OF   PETROLEUM   AND    ASPHALT 

different  results  after  treatment  with  the  same  oil  as  shown  by 
analysis.  The  only  rational  explanation  for  these  differences 
would  seem  to  lie  in  the  relative  moisture  contents  of  the  surface 
at  the  time  of  treatment.  Variations  in  the  character  of  the 
roadstone  will,  of  course,  exert  an  effect  upon  the  way  an  oil 
will  incorporate  with  the  road,  as  some  rock  powders  produce  a 
tough  elastic  mixture  while  others  are  crumbly  when  mixed 
with  oil. 

The  main  object  in  oiling  a  macadam  road  is  to  obtain  an  even 
coating,  which  shall  be  well  absorbed  by  the  road  surface.  The 
application  of  a  large  excess  of  oil  is  sure  to  make  the  surface 
sticky  and  disagreeable.  A  covering  of  sharp  sand  or  one-half 
inch  stone  screenings  should  be  applied  after  the  oil  has  been 
allowed  to  penetrate  as  much  as  possible,  in  order  to  take  up 
all  excess,  and  the  surface  thus  formed  may  then  be  rolled  until 
well  compacted,  additional  sand  or  screenings  being  thrown  on 
wherever  the  oil  shows  a  tendency  to  force  its  way  to  the  sur- 
face and  produce  a  sticky  condition.  Sometimes  two  or  three 
courses  of  oil  and  screenings  are  applied.  It  is  usually  con- 
sidered better  practice  to  allow  the  freshly  oiled  road  to  dry  out 
to  some  extent  before  applying  the  top  dressing,  but  in  cases 
where  it  is  impossible  to  keep  traffic  away  either  one-half  the 
width  of  the  road  may  be .  treated  at  one  time  or  the  sand  or 
screenings  may  be  applied  at  once.  If  the  oil  is  well  absorbed  it 
is  not  necessary  to  employ  the  roller,  as  ordinary  traffic  will 
consolidate  the  surface  in  the  course  of  time. 

The  objections  which  have  been  urged  against  oiled  macadam 
roads  are  that  the  oil  has  an  unpleasant  odor,  that  it  is  tracked 
onto  pavements  and  into  houses,  that  particles  of  the  road 
surface  thrown  up  by  the  wheels  of  moving  vehicles  are  inju- 
rious to  clothes,  that  rubber  tires  are  injured,  that  a  disagree- 
able mud  is  formed  in  wet  weather  ruinous  to  the  varnish  on 
vehicles,  and  that  the  tractive  resistance  of  the  road  is  in- 
creased. If  the  right  kind  of  oil  is  applied  under  proper  con- 
ditions most  of  these  objections  can  be  overcome.  A  good 
asphaltic  residual  oil  should  have  but  a  faint  odor  and  even 


214  DUST   PREVENTIVES   AND   ROAD    BINDERS 

the  odor  of  cut-back  products  should  shortly  disappear  as  the 
lighter  constituents  volatilize.  Application  of  too  much  oil  or 
the  presence  of  too  much  fine  material  on  the  road  surface  are 
the  most  frequent  causes  of  the  remaining  objections.  In  a 
finished  oiled  macadam  the  fine  material  should  be  just  satu- 
rated and  no  more,  and  this  can  be  controlled  by  sanding.  If 
this  is  done  the  oil  should  not  track  and  particles  of  the  oiled 
road  surface  should  not  be  more  injurious  to  clothes  than  any 
other  dirt.  A  proper  mixture  of  oil  and  stone  dust  should 
leave  no  stain  when  placed  upon  a  piece  of  cloth.  The  oil 
may  of  course  be  tracked  shortly  after  being  applied  and  while 
it  is  penetrating  the  road  surface.  At  this  time,  as  has  been 
stated,  the  freshly  oiled  surface  should  be  closed  to  traffic.  So 
far  as  can  be  learned,  an  oiled  road  does  not  injure  rubber  tires 
unless  a  great  excess  of  oil  is  present,  so  that  this  objection 
may  be  easily  overcome.  The  presence  of  too  much  fine  mate- 
rial upon  the  road  surface  is  often  responsible  for  the  forma- 
tion of  a  disagreeable  mud  in  wet  weather,  and  this  together 
with  the  use  of  too  much  oil  causes  the  increased  tractive  re- 
sistance often  commented  upon.  If  proper  precautions  are 
taken,  however,  and  the  right  methods  followed,  an  oiled  mac- 
adam surface  should  be  for  the  time  being  smooth,  dustless, 
waterproof  and  resilient.  It  should  have  no  disagreeable  odor 
to  speak  of  and  its  appearance  should  be  pleasing  and  restful 
to  the  eyes,  being  of  a  seal  brown  color  which  does  not  produce 
the  glary  effect  of  an  untreated  macadam  in  bright  sunlight. 
In  dry  weather  it  should  show  a  crust  of  asphalt-like  surface. 
Long  continued  rains  and  especially  alternate  freezing  and  thaw- 
ing will  in  a  short  time  destroy  the  bond  of  this  crust  to  a  great 
extent,  and  the  treatment  will  ordinarily  have  to  be  repeated  at 
the  beginning  of  the  next  dusty  season. 

Construction  of  Oil  Earth  Roads.  —  Oiled  earth  roads  have 
been  most  successfully  constructed  in  California  where,  as  has 
been  stated,  climatic  conditions  are  favorable  and  the  oil  is 
best  suited  for  such  work.  The  methods  originated  and 
employed  in  this  state  are  of  great  interest,  and  have  been 


APPLICATION   OF  PETROLEUM   AND   ASPHALT  215 

followed  quite  closely  by  experimenters  in  other  sections  of 
the  country.  In  the  earlier  work  such  promising  results  fol- 
lowed the  application  of  oil  to  earth  road  surfaces  that  attempts 
were  soon  made  to  further  improve  matters  by  incorporating 
the  oil  in  the  body  of  the  road,  with  the  hope  of  obtaining  per- 
manent results. 

One  of  the  simplest  and  cheapest  methods  of  building  such  a 
road  is  to  first  cut  it  out  to  the  desired  cross  section.  The 
subgrade  should  be  well  compacted  and  all  weak  spots  and 
holes  filled  with  sound  material  and  thoroughly  consolidated. 
Oil  may  then  be  applied  to  this  base  at  the  rate  of  approxi- 
mately one  gallon  per  square  yard,  after  which  a  road  grader 
is  employed  to  return  the  earth  which  has  previously  been 
removed  to  the  sides  of  the  road.  While  this  is  being  done, 
a  drag  attached  to  the  rear  of  the  grader  smooths  the  earth 
over  the  oil  to  a  depth  of  four  or  five  inches.  The  road  is 
then  thoroughly  rolled  and  opened  to  traffic.  The  grader  and 
drag  should  be  used  upon  the  road  to  smooth  it  up  from  time 
to  time  until  the  oil  comes  to  the  surface  under  the  action  of 
traffic.  Such  a  method  has  been  described  by  Eldridge  *  as  pro- 
ducing good  results. 

Thorough  incorporation  of  the  oil  with  the  earth  is  one  of  the 
most  important  factors  to  be  considered  in  the  construction 
of  an  oiled  earth  road,  and  if  this  is  not  accomplished  an 
uneven  surface  will  be  produced  which  is  soft  and  sticky  in 
spots.  A  disk  harrow  and  road  grader  are  of  great  service  in 
securing  a  uniform  mixture,  the  harrow  cutting  up  and  pulveriz- 
ing the  clods  of  earth  and  the  grader  turning  and  rolling  it  from 
side  to  side.  It  has  been  found  that  the  application  of  water  to 
the  roadway  during  process  of  construction  is  often  a  great  aid 
in  mixing  as  it  keeps  the  earth  in  a  finely  divided  state,  thus 
allowing  the  oil  to  permeate  the  entire  mass. 

Another  accessory  for  mixing  and  compacting  the  road  which 
has  been  extensively  used  in  California,  is  known  as  the  rolling 

*  Biennial  Report,  Department  of  Highways,  State  of  California,  December, 
1906. 


2l6  DUST   PREVENTIVES   AND    ROAD  BINDERS 


APPLICATION   OF   PETROLEUM   AND    ASPHALT  2 1/ 

tamper.  The  construction  of  this  machine,  a  type  of  which  is 
shown  in  Fig.  19,  was  suggested  by  the  effect  produced  by  a 
large  flock  of  sheep  walking  over  a  newly  plowed  road.  After 
the  sheep  had  passed  it  was  noticed  that  the  road  had  been 
packed  extremely  hard.  It  will  be  seen  that  the  rolling  tamper 
has  the  form  of  a  roller,  from  the  circumference  of  which  pro- 
ject a  large  number  of  tampers  which  act  like  so  many  feet 
walking  over  the  earth  and  packing  it  down.  Owing  to  its 
peculiar  construction  this  roller,  under  favorable  conditions, 
consolidates  the  road  from  the  bottom  up,  instead  of  from  the 
top  down  as  in  the  case  of  other  rollers.  The  effect  is  much  the 
same  as  would  be  produced  by  the  flock  of  sheep  passing  over 
the  road.  For  this  reason  it  is  sometimes  called  the  sheeps- 
foot  roller.  As  each  of  the  tampers  sinks  into  the  road  it  com- 
pacts a  small  portion  of  soil  beneath  it,  and  as  the  head  is  larger 
than  the  shank,  some  dirt  falls  back  into  the  hole  formed  when 
it  is  pulled  out.  In  this  way  the  earth  is  consolidated  from  the 
bottom  up  as  the  roller  is  passed  back  and  forth,  the  roller 
eventually  riding  entirely  upon  the  surface.  This  machine  is 
better  adapted  for  use  on  sandy  or  loamy  soils  than  on  clayey 
soils  as  the  latter  are  apt  to  pick  up  and  pack  between  the 
shanks  of  the  roller  until  it  fills  up  solid.  A  self  cleaning  de- 
vice should  overcome  this  difficulty  to  a  great  extent. 

Another  type  of  rolling  tamper,  quite  similar  to  the  above, 
which  has  been  used  in  the  east,  consists  of  a  series  of  cast  iron 
toothed  discs,  loosely  journaled  upon  an  axle.  The  machine 
weighs  about  5,000  pounds  and  each  tooth  has  a  surface  area 
of  about  eight  square  inches.  The  weight  upon  each  indi- 
vidual tooth  as  it  passes  over  the  road  amounts  to  about  800 
pounds,  the  pressure  exerted  being  therefore  about  100  pounds 
per  square  inch. 

When  employing  a  rolling  tamper  the  following  general 
method  has  been  employed  in  constructing  what  is  commonly 
known  as  a  petrolithic  earth  road. 

The  road  is  first  plowed  up  to  a  depth  of  six  inches  and  properly 
crowned.  All  clods  and  lumps  are  thoroughly  broken  up  by 


218 


DUST   PREVENTIVES   AND    ROAD    BINDERS 


FIG.  20.     Petrolithic  Spike  Disc  Harrow. 

means  of  a  harrow,  preferably  spike  toothed,  such  as  shown  in 
Fig.  20,  and  the  roadway  well  sprinkled  with  water.  The 
tamping  roller  is  then  used  to  compact  the  loose  earth  from  the 
bottom  up,  to  the  depth  of  two  inches.  After  the  under  surface 
is  made  firm  by  this  means,  a  heavy  asphaltic  oil  is  applied  at 
the  rate  of  from  one  to  one  and  one-half  gallons  per  square  yard, 
and  a  cultivator  passed  over  the  road  until  the  oil  and  earth  are 
thoroughly  mixed.  The  tamper  is  then  used  again  and  the 
road  further  compacted  until  only  one  and  one-half  inches  of 
loose  material  remain  on  top.  This  is  lightly  harrowed  and 
sufficient  water  added  to  moisten  it.  Oil  is  again  applied,  the 
surface  rolled  with  the  tamper  until  firm,  and  finally  ironed  down 
with  an  ordinary  roller,  additional  application  of  earth  being 
applied  wherever  necessary  to  take  up  any  excess  of  oil.  A  road 
constructed  in  this  manner  will  require  from  two  to  three  gallons 
per  square  yard.  Where  the  natural  soil  is  very  clayey  it  may 
be  well  to  modify  it  by  bringing  in  some  sandy  soil  from  the 


APPLICATION    OF   PETROLEUM   AND    ASPHALT  219 

outside,  if  such  can  be  obtained,  and  mixing  the  two  together 
before  applying  the  oil.  An  exceedingly  sandy  soil  will  on  the 
other  hand  be  benefited  by  the  addition  of  a  small  amount  of 
clayey  material. 

When  an  oil  containing  asphaltic  hydrocarbons  is  applied  to 
a  road,  it  is  probable  that  these  products  are  selectively  held 
by  the  finer  products  constituting  the  body  of  the  road.  In 
fractionating  crude  petroleum  by  capillary  filtration,  Day*  has 
demonstrated  the  following  facts. 

(1)  "  When  petroleum  is  allowed  to  rise  in  a  tube  packed  with 
fuller's  earth,  there  is  a  decided  fractionation  of   the  oil,  the 
fraction  at  the  top  of  the  tube  being  of  lower  specific  gravity 
than  at  the  bottom." 

(2)  "  When  petroleum  is  allowed  to  rise  in  a  tube  packed  with 
fuller's  earth,  the  paraffin  hydrocarbons  tend  to  collect  in  the 
lightest  fraction  at  the  top  of  the  tube  and  the  unsaturated 
hydrocarbons  at  the  bottom." 

Similar  results  are  undoubtedly  produced  under  the  action  of 
traffic,  especially  in  the  case  of  oiled  earth  roads,  and  account 
for  the  rather  rapid  volatilization  of  light  oils  and  also  for  the 
slimy  surface  condition  of  roads  treated  with  oils  containing 
considerable  quantities  of  the  less  volatile  paraffin  hydrocarbons. 

Roads  constructed  with  earth  and  oil  have  not  proven  as 
entirely  successful  as  was  first  expected  even  in  the  State  of 
California,  and  at  the  present  time  it  seems  extremely  doubtful  if 
they  will  ever  prove  to  be  a  satisfactory  type  of  road  in  the 
eastern  states  when  the  above  method  is  employed.  In  the  first 
place  for  this  sort  of  work  it  is  quite  necessary  that  the  oil 
be  capable  of  hardening  after  application  to  form  a  semisolid 
product  which  will  increase  the  mechanical  stability  of  the 
road  and  prevent  rutting.  California  oils  are  the  only  natural 
oils  which  will  do  this,  and  the  author  knows  of  no  residual  or 
cut-back  products  produced  outside  of  California  which  can  be 
recommended  for  this  purpose.  Even  the  California  oil  when 

*  "The  Production  of  Petroleum  in  1907,"  U.  S.  Geological  Survey,  Department 
of  the  Interior,  1908. 


22O  DUST   PREVENTIVES   AND    ROAD    BINDERS 

incorporated  in  the  body  of  the  road  to  the  depth  of  five  or  six 
inches  requires  a  long  time  to  harden,  and  because  of  this,  much 
complaint  has  been  made  in  regard  to  the  great  increase  in 
tractive  resistance  of  the  road  surface  due  to  the  presence  of  the 
oil.  For  the  first  year  or  so  the  road  ruts  badly  and  should  be 
continually  dragged  and  in  some  cases  spiked  up  and  turned  over. 
After  completion  the  road  surface  becomes  softer,  owing  to  the 
tendency  of  the  oil  to  work  upward  under  the  action  of  traffic. 
In  the  course  of  time,  however,  a  gradual  hardening  takes  place 
and  satisfactory  results  are  eventually  produced. 

At  the  present  time  the  cost  of  transporting  California  oil 
to  the  eastern  states  is  prohibitive  for  ordinary  road  work.  In 
some  few  cases,  however,  this  has  been  done  for  the  purpose  of 
ascertaining  whether  or  not  the  California  work  could  be  dupli- 
cated under  existing  conditions.  The  results  obtained  have 
apparently  answered  this  question  in  the  negative,  for  it  has  been 
found  that  climatic  conditions  make  it  almost  an  impossibility 
to  keep  the  road  in  a  passable  state  during  the  hardening  process. 
This  is  particularly  true  in  winter  weather  when  owing  to 
alternate  freezing  and  thawing  the  road  is  churned  up  under  the 
action  of  traffic  into  heavy  oily  mud  to  its  entire  depth,  so  that 
for  a  number  of  months  in  the  year  it  is  more  or  less  a  slough. 
Where  the  climate  is  similar  to  that  of  California,  however, 
there  seems  to  be  no  reason  why  as  satisfactory  results  cannot 
be  obtained  as  in  that  state,  providing  that  California  or  simi- 
lar oils  are  used. 

If  the  oiled  earth  road  is  to  prove  successful  in  the  eastern 
states,  it  is  evident  that  a  heavy  semisolid  or  solid  binder  will 
have  to  be  employed  which  immediately  after  application  will 
produce  the  desired  mechanical  stability.  In  order  to  obtain 
a  good  mixture  this  would  necessitate  heating  both  the  earth 
and  bitumen  and  mixing  them  together  before  they  are  applied 
to  the  road.  This  would  entail  considerable  expense  and  where 
rock  is  available  would  not  be  necessary,  for  a  bituminous 
macadam  could  be  constructed  at  a  very  slightly  increased  cost 
and  in  many  respects  would  be  preferable.  In  fact  in  Cali- 


APPLICATION   OF   PETROLEUM   AND   ASPHALT  221 

fornia  the  oil-earth  road  is  undergoing  a  process  of  evolution 
leading  to  the  use  of  broken  stone  in  a  type  of  road  commonly 
known  as  the  petrolithic  macadam.  This  in  itself  is  good  evi- 
dence that  even  under  the  most  favorable  conditions  the  oil- 
earth  road  has  not  been  ,  found  altogether  satisfactory.  A 
description  of  this  type  of  road  will  be  given  later. 

Construction  of  Oil  Gravel  Roads.  —  Oil  is  applied  to  a  gravel 
road  during  construction  in  a  manner  quite  similar  to  the  sur- 
face treatment  already  described,  but  certain  points  in  regard 
to  the  method  of  construction  should  be  noted.  These  facts 
are  well  presented  by  Eldridge  in  the  report  previously  men- 
tioned which  contains  specifications  used  in  certain  parts  of 
California  for  the  construction  of  oiled  gravel  streets.  Certain 
portions  of  these  specifications  in  condensed  form  are  given 
below  for  the  purpose  of  emphasizing  the  most  essential 
points. 

Before  placing  the  gravel,  the  subsurface  must  be  brought  to 
grade  and  rolled  with  a  roller  weighing  not  less  than  two  hundred 
and  fifty  pounds  per  inch  width  of  tire.  Upon  this  subsurface 
two  layers  of  good  gravel  should  be  applied,  the  bottom  layer 
having  a  thickness  of  five  inches  and  the  top  a  thickness  of  three 
inches  after  being  rolled.  The  first  layer  should  contain  no  stones 
larger  than  two  and  one-half  inches  in  greatest  diameter.  The 
gravel  must  be  uniformly  spread  on  the  roadway  and  well 
moistened,  rammed  one  foot  from  the  gutter  or  curb,  and  the 
remaining  portion  rolled  with  a  roller  of  the  type  before  specified. 
All  depressions  must  be  promptly  filled,  moistened  and  again 
rolled,  the  rolling  being  continued  until  the  surface  will  not 
yield  under  the  roller.  On  this  surface  the  top  layer  of  gravel, 
free  from  all  stones  larger  than  one  inch  in  greater  diameter, 
should  be  applied  and  compacted  in  the  same  manner  as  the 
first  layer.  Oil  should  then  be  evenly  distributed  over  the  entire 
surface  at  the  rate  of  one-half  gallon  per  square  yard  and  cov- 
ered with  clean,  sharp  sand  until  no  oil  can  be  seen.  After  the 
lapse  of  not  less  than  twelve  hours,  another  application  of  oil 
should  be  made  and  sand  distributed  in  the  same  manner  and 


222  DUST   PREVENTIVES   AND    ROAD    BINDERS 

the  whole  surface  rolled  until  unyielding  to  the  roller,  as  before 
described. 

Construction  of  Petrolithic  Macadam.  —  As  has  been  stated, 
the  petrolithic  macadam  is  largely  replacing  the  early  petro- 
lithic  earth  road  in  California.  While  various  methods  of  con- 
struction are  employed,  they  are  all  quite  similar  and  the 
following  description  may  be  considered  as  typical  of  this  class 
of  road. 

The  roadbed  after  being  graded  and  crowned  is  plowed  to  a 
depth  of  six  inches  and  the  soil  thoroughly  pulverized  and  culti- 
vated as  described  under  the  construction  of  oil-earth  roads. 
The  road  is  then  well  sprinkled  with  water,  after  which  oil  is 
applied  at  the  rate  of  from  one-half  to  three-fourths  gallon  per 
square  yard  according  to  the  depth  of  crushed  stone  which 
is  afterwards  to  be  used.  The  stone  should  run  from  two  to 
four  inches  in  depth  and  the  quantity  of  oil  used  in  the  con- 
struction of  the  foundation  should  vary  inversely  with  the 
amount  of  stone. 

After  the  oil  has  been  applied  the  road  is  thoroughly  culti- 
vated with  the  addition  of  water  as  needed.  A  second  appli- 
cation of  oil  is  then  made  at  the  same  rate  as  the  first  and  the 
road  recultivated  as  before.  A  third  application  of  oil  follows 
this  and  the  cultivation  is  again  repeated  until  a  thorough  mix- 
ture of  oil  and  earth  has  been  obtained.  Water  is  frequently 
.sprinkled  upon  the  road  throughout  this  process  and  should 
finally  produce  an  almost  muddy  condition.  The  road  is  then 
tamped  with  the  rolling  tamper,  above  described,  until  it  is  hard 
and  solid,  water  being  employed  as  often  as  necessary  to  keep 
the  soil  in  the  best  condition  for  working.  While  the  roadway  is 
being  consolidated  the  tamper  should  be  continuously  followed 
by  a  cultivator  set  so  as  not  to  disturb  the  sub-base  already 
tamped.  It  is  necessary  that  the  cultivator  be  reset  from  time 
to  time,  the  purpose  being  simply  to  prevent  a  too  rapid  con- 
solidation of  the  road  and  assist  the  tamper  in  compacting  from 
the  bottom  up. 

After  the  roadway  is  hard  and  firm  two  to  four  inches  of  one 


APPLICATION    OF   PETROLEUM    AND    ASPHALT  223 

and  one-half  inch  crushed  rock  is  spread  and  cultivated  into  the 
top  two  inches  of  oiled  earth,  which  should  serve  as  a  binder. 
A  fourth  coat  of  oil  is  then  applied  at  the  rate  of  from  one-half 
gallon  per  square  yard  when  two  inches  of  stone  are  used  to  one 
gallon  per  square  yard  when  four  inches  of  stone  are  used.  The 
oil  and  rock  and  oiled  earth  are  then  cultivated  until  thor- 
oughly mixed,  and  tamped  with  the  rolling  tamper  until  hard 
and  unyielding.  At  this  point  the  surface  while  hard  is  quite 
rough  with  the  marks  of  the  tamper.  A  fifth  application  of  oil 
is  then  applied  at  the  rate  of  one-fourth  gallon  per  square  yard, 
and  a  coat  of  one-half  inch  stone  screenings  spread  over  the 
oiled  surface.  This  course  is  sprinkled  with  water  and  rolled 
into  the  surface  of  the  pavement  with  the  rolling  tamper.  The 
whole  road  is  then  smoothed  off  with  an  ordinary  roller. 

In  this  work  the  top  coat  of  screenings  should  not  be  oiled,  as 
the  oil  below  will  be  sufficient  to  saturate  it  under  the  action  of 
the  roller.  It  is  important  to  thoroughly  coat  the  large  stone 
with  oil  and  oiled  earth  so  that  the  upper  surface  is  absolutely 
homogeneous,  and  it  is  of  course  necessary  to  use  a  good  grade 
of  asphaltic  oil.  The  heaviest  oil  which  can  be  mixed  in  the 
manner  described  is  to  be  preferred  and  it  should  be  applied 
hot.  The  total  quantity  of  oil  required  will  run  from  about 
2^£  to  3  gallons  per  square  yard  depending  upon  the  amount  of 
stone  used.  In  California  it  is  claimed  that  such  work  can  be 
done  for  approximately  90  cents  per  square  yard  when  four 
inches  of  stone  are  applied. 

Oil  Asphalt  Macadam  Construction.  —  There  are  two  methods 
commonly  employed  in  the  construction  of  oil  asphalt  maca- 
dam, known  as  the  penetration  method  and  the  mixing  method. 
These  will  be  discussed  in  detail  in  Chapter  XII  under  tar 
macadam  construction,  as  the  modus  operandi  is  quite  simi- 
lar for  both  oils  and  tars.  In  brief  the  penetration  method 
consists  in  first  building  an  ordinary  macadam  road  without 
the  application  of  screenings  to  the  top  course.  This  course 
should,  however,  be  thoroughly  compacted  with  a  roller,  after 
which  hot  oil  is  applied  at  the  rate  of  approximately  one  and 


224  DUST   PREVENTIVES   AND    ROAD    BINDERS 

one-half  gallons  per  square  yard.  The  oil  penetrates  the  road 
and  should  cover  the  stones  to  a  depth  of  about  two  inches, 
after  which  a  light  coat  of  clean  stone  chips  is  applied  in  suffi- 
cient quantity  to  fill  the  surface  voids  after  rolling.  A  seal  coat 
of  oil  is  then  applied  at  the  rate  of  approximately  one-half 
gallon  per  square  yard  and  enough  screenings  spread  on  to 
take  up  all  excess  of  oil  and  form  a  dense  smooth  surface  when 
rolled. 

In  the  mixing  method  the  upper  course  of  stone  is  mixed 
with  oil  before  being  laid.  The  oil  should  invariably  be  heated 
and  it  is  often  desirable  to  heat  the  stone  also.  Mixing  may 
be  done  by  hand  or  machinery  and  the  bitumen  coated  stone, 
while  still  warm,  spread  upon  the  road  to  a  depth  of  from  two 
to  three  inches.  After  rolling,  a  flush  coat  of  oil  is  applied  to  the 
road  surface,  and  the  road  finished  with  screenings  as  in  the 
penetration  method. 

In  oil  macadam  construction  an  oil  product  having  con- 
siderable mechanical  stability  should  be  employed,  and  one 
approaching  the  consistency  of  an  asphaltic  cement,  such  as 
used  in  the  binder  course  of  an  asphalt  pavement,  will  produce 
the  best  results.  In  the  penetration  method  such  a  material 
cannot  well  be  applied  as  it  will  solidify  upon  coming  in  con- 
tact with  the  cold  stone  and,  therefore,  fail  to  penetrate  the  upper 
course  to  the  desired  extent.  If  this  happens  a  heavy  coat  of 
sticky  bitumen  will  remain  upon  the  road  surface  which  will 
have  to  be  covered  with  a  large  amount  of  screenings.  Under 
the  action  of  traffic,  the  whole  surface  of  bitumen  and  screen- 
ings is  likely  to  pick  up  and  peel  off  in  patches.  On  the  other 
hand,  if  too  soft  a  bitumen  is  employed  the  road  surface  will  be 
soft  and  wavy  and  will  rut  badly.  Tractive  resistance  will  be 
greatly  increased  and  the  oil  will  continually  sweat  to  the  sur- 
face under  the  action  of  traffic  and  the  heat  of  the  sun.  Fluid 
residual  oils  are  as  a  rule  unsuited  for  this  sort  of  work  because 
they  have  no  tendency  to  harden  after  application.  The  softer 
semisolid  bitumens  and  cut-back  products  may,  however,  give 
satisfaction,  if  carefully  applied. 


APPLICATION   OF  PETROLEUM   AND   ASPHALT  225 

In  the  mixing  method  it  is  possible  to  use  an  oil  asphalt  or 
asphaltic  cement  having  sufficient  original  consistency  to  pro- 
duce a  firm  solid  road  almost  immediately  after  it  has  been 
applied.  These  points  will  be  further  discussed  in  the  chapter 
on  Selection.  Both  the  penetration  and  the  mixing  methods 
may  be  employed  when  resurfacing  old  macadam  roads,  as  will 
be  described  later. 

Rock  Asphalt  Macadam.  —  In  the  construction  of  a  rock 
asphalt  macadam  the  subgrade  is  prepared  in  the  same  manner 
as  for  an  ordinary  macadam.  All  soft  spots*  should  be  filled 
with  sound  material  and  the  whole  rolled  until  well  compacted 
and  solid.  The  lower  course  of  broken  stone  should  then  be 
laid  and  rolled  in  the  usual  manner,  enough  screenings  being 
applied  to  produce  an  unyielding  surface.  Upon  this  foundation 
should  be  spread  a  two  and  one-half  inch  course  of  crushed 
rock  preferably  ranging  in  size  from  one  to  two  inches.  This 
course  should  be  rolled  only  sufficiently  to  produce  a  smooth 
even  surface  and  no  attempt  made  to  reduce  the  voids  in  any 
other  manner.  Rock  asphalt  should  then  be  thrown  on  from 
dumping  boards  by  means  of  shovels  and  raked  over  the  sur- 
face to  a  uniform  depth  of  one-half  inch.  It  should  never  be 
dumped  directly  upon  the  road  from  a  wagon.  After  applica- 
tion it  should  be  rolled  into  the  upper  course  as  thoroughly  as 
possible,  care  being  taken  that  loose  earth  and  dirt  are  not  brought 
upon  the  surface  by  the  roller.  A  one-inch  coat  of  the  rock 
asphalt  is  next  applied  in  the  same  manner  as  before  and 
well  rolled.  Sometimes  it  may  be  advisable  to  apply  the  rock 
asphalt  in  a  single  one  and  one-half  inch  layer. 

The  roller  should  be  kept  moving  back  and  forth  parallel  to 
the  axis  of  the  roadway  and  worked  from  the  outer  edge  to 
the  crown,  as  in  ordinary  macadam  construction.  If,  in  the 
last  coat,  the  roller  tends  to  pick  up  the  rock  asphalt,  its 
wheels  may  be  dusted  with  a  light  coating  of  cement  or  rubbed 
with  a  cloth  saturated  with  kerosene.  After  rolling  for  some 
time  the  surface  may  begin  to  crack,  if  the  weather  is  cool, 
in  which  case  it  is  well  to  discontinue  the  rolling  for  a  while 


226  DUST   PREVENTIVES  AND   ROAD  BINDERS 

and  start  again  when  the  surface  is  warmer  and  more  pliable. 
A  tandem  roller  is  better  adapted  for  this  sort  of  work  than  the 
ordinary  three  wheel  road  roller,  although  the  latter  is  necessary 
for  rolling  the  stone  courses. 

Best  results  can  be  obtained  in  warm  dry  weather  and  in  no 
case  should  the  temperature  fall  below  5°  C.  while  the  pave- 
ment is  being  laid.  The  broken  stone  of  the  wearing  course 
should  be  clean  and  dry  to  facilitate  adhesion,  and  of  fairly 
uniform  size  so  that  enough  voids  will  be  present  to  allow  the 
rock  asphalt  to  be  forced  into  the  road.  When  first  opened  to 
traffic  the  cushion  of  rock  asphalt  is  apt  to  rut,  but  finely  irons 
out  into  a  smooth  firm  surface  not  unlike  that  of  a  sheet  as- 
phalt pavement,  provided  the  bitumen  is  of  proper  consistency 
and  the  sand  aggregate  fairly  well  graded.  A  product  carrying 
from  7  to  10  per  cent  bitumen  is  best  suited  for  this  work. 
The  percentage  of  bitumen  should  never  fall  below  6  per  cent. 
While  the  wearing  course  may  be  composed  of  the  rock  asphalt 
alone,  if  the  proportion  and  character  of  bitumen  is  just  right 
and  the  sand  aggregate  well  graded,  it  is  preferable  to  have  the 
upper  course  of  stone  take  up  the  wear  and  tear  of  traffic  and 
the  rock  asphalt  simply  fill  the  voids  in  the  road  and  act  as 
a  binder  for  the  larger  stone.  As  traffic  tends  to  force  the 
material  into  the  road  even  more  than  rolling,  it  is,  however, 
advisable  to  leave  a  thin  cushion  coat  of  the  material  on  the 
surface  just  after  completion. 

Rock  asphalt  may  be  employed  in  the  resurfacing  of  old 
macadam  roads  in  much  the  same  manner  as  described  for  the 
construction  of  new  roads.  In  this  case  the  old  macadam 
should  first  be  spiked  up,  all  holes  and  depressions  filled  and 
the  road  brought  to  proper  crown,  after  which  a  course  of  clean 
crushed  rock  is  laid  and  compacted  as  described  for  the  wearing 
course  in  construction  work.  Application  of  the  rock  asphalt 
is  then  made  and  the  surface  finished  as  above  described.  If 
the  road  cannot  be  closed  to  traffic  during  resurfacing,  it  will 
be  necessary  to  apply  the  rock  asphalt  to  one  side  at  a  time,  in 
which  case,  in  order  to  avoid  an  unsightly  joint  along  the  middle 


APPLICATION    OF   PETROLEUM   AND    ASPHALT  22/ 

of  the  road,  the  point  of  over-lapping  should  not  be  rolled  until 
last.  Care  must  be  taken  that  no  dust  or  other  extraneous 
material  finds  its  way  into  this  joint  or  otherwise  the  two  sides 
will  not  bond  together  upon  rolling. 

When  natural  rock  asphalt  is  close  at  hand  the  cost  of  con- 
structing a  rock  asphalt  macadam  is  but  little  more  than  ordi- 
nary macadam  work  in  that  locality.  If  the  material  has  to 
be  shipped  for  any  considerable  distance,  however,  it  does  not 
make  an  economical  binder,  as  the  freight  on  the  90  to  93  per  cent 
of  sand  which  it  contains  raises  the  cost  out  of  proportion  to 
the  results  obtained,  as  compared  with  other  binders.  If  it 
is  desired  to  build  this  type  of  road  in  such  localities  it  will  be 
found  cheaper  to  obtain  a  local  sand  and  mix  it  hot  with  a  soft 
asphaltic  cement  in  suitable  proportions.  This  mixture  may 
be  used  in  exactly  the  same  manner  as  the  natural  rock  asphalt, 
and  has  the  advantage  of  being  absolutely  uniform  and  subject 
to  control  by  the  road  engineer.  For  the  preparation  of  such 
a  material  recourse  should  be  had  to  a  mechanical  mixer  of  the 
type  used  in  the  preparation  of  an  ordinary  asphalt  surface 
mixture.  It  iriay  be  mixed  by  hand  if  preferred,  but  this  will 
cost  more  in  the  long  run  than  mechanical  mixing  if  any  con- 
siderable amount  of  work  is  to  be  done. 

Summary  and  Conclusions.  —  In  this  chapter  the  surface 
treatment  and  construction  of  earth  gravel  and  broken  stone 
roads  with  oil  and  oil  products  have  been  described  in  some 
detail.  In  comparing  the  various  types  of  oiled  roads  it  may 
be  said  that  in  general  the  oil  asphalt  macadam  constructed 
according  to  the  mixing  method  will  in  the  long  run  prove  the 
most  satisfactory  and  economical.  Such  roads  should  not  cost 
at  the  outside  over  20  to  25  cents  per  square  yard  in  excess  of 
ordinary  macadam,  and  15  cents  may  often  cover  this  additional 
cost.  The  other  types  of  road  have  their  field  of  usefulness, 
however,  and  may  in  some  instances  be  even  preferable  to  the 
asphalt  macadam.  Surface  applications  of  a  good  binding  oil 
will  invariably  prolong  the  life  of  a  road,  and  even  the  asphalt 
macadam  will  be  greatly  benefited  by  such  treatments  made 


228  DUST  PREVENTIVES    AND    ROAD   BINDERS 

from  time  to  time  as  occasion  requires.  All  kinds  of  properly 
oiled  roads  are  practically  noiseless,  waterproof  and  resilient 
and  for  the  time  being,  dustless.  In  the  course  of  time  dust 
will,  of  course,  accumulate  on  the  surface  and  additional  light 
applications  of  oil  may  then  be  required.  Automobile  traffic 
will  cause  far  less  damage  to  an  oil  treated  road  than  to  the 
same  untreated  road.  There  are  two  enemies,  however,  that 
will  have  to  be  assiduously  guarded  against.  These  are  water 
and  frost  action.  No  matter  how  carefully  the  oil  has  been 
selected  and  applied,  failure  will  invariably  result  if  the  road 
is  not  properly  drained  both  at  the  surface  and  foundation. 

In  conclusion  mention  may  be  made  of  one  use  of  oil  which, 
while  not  directly  bearing  upon  road  preservation,  is  closely 
associated  with  it.  This  is  the  application  of  a  thin  cushion 
of  oiled  earth  to  the  plank  flooring  of  bridges.  Such  treatment 
will  be  found  to  materially  prolong  the  life  of  the  wood  be- 
neath, which  is  thus  protected  from  the  wear  and  tear  of  steel 
shod  traffic.  For  this  purpose  a  heavy  oil  which  will  bind  the 
earth  particles  firmly  together  and  form  a  rubbery  cushion  is  to 
be  preferred. 


CHAPTER  XI. 
TAR  AND  TAR  PRODUCTS. 

WHILE  the  term  tar  is  applied  to  distillates  produced  in  the 
destructive  distillation  of  various  organic  materials,  as  stated 
in  Chapter  VII,  it  is  only  those  produced  from  coal  and  petro- 
leum that  are  of  particular  interest  in  the  treatment  of  roads. 
Coal  tars  may  be  divided  into  three  classes  known  as  (i)  gas 
house  tars,  (2)  coke  oven  tars  and  (3)  blast  furnace  tars,  of 
which  the  first  two  are  of  the  most  common  occurrence  and  by 
far  the  most  important.  Blast  furnace  tars  are  not  at  present 
a  factor  in  road  treatment  and  need  not  be  considered.  Petro- 
leum tars  may  be  classified  as  (i)  water  gas  tars,  and  (2)  true 
oil  gas  tars,  according  to  their  method  of  manufacture.  As 
in  the  case  of  oils,  considerable  variations  exist  in  both  the 
chemical  and  the  physical  properties  of  tars,  although  here  the 
differences  are  more  directly  related  to  the  process  of  manu- 
facture than  to  the  locality  in  which  they  are  produced.  The 
properties  of  the  material  distilled  however  exert  considerable 
influence  upon  the  character  of  tar. 

The  total  production  of  coal  tar  and  petroleum  tar  in  the 
United  States  during  1908  amounted  to  110,430,663  gallons 
valued  at  $2,766,700.  This  is  about  80,000,000  gallons  less 
than  that  produced  in  the  United  Kingdom  during  1906  from 
coal  alone.  The  amount  of  coal  coked  and  the  tar  produced 
therefrom  in  the  United  States  during  the  years  1903  to  1908 
are  given  in  the  following  table. 

COAL  COKED  AND  TAR  PRODUCED  IN  THE  UNITED  STATES. 


Year. 

Coal    Coked, 
Short  Tons. 

Tar  Produced 
and  Sold, 
Gallons. 

IQO3 

t;  843  ?q8 

62,064,703 

IQOA.  . 

v.o^S.io 

69,408,085; 

1  9O?  .  . 

8,187,812 

80,022,043 

1007.  .  . 

11,490,661 

103x77,760 

0 

1908  

9,252,978 

101,261,829 

229 


230  DUST   PREVENTIVES    AND    ROAD    BINDERS 

The  notable  decrease  for  1908  as  compared  with  1907  was 
due  to  the  prevailing  business  depression,  which  materially 
curtailed  the  demand  for  coke.  Had  conditions  been  normal 
an  increase  in  production  would  undoubtedly  have  been  shown 
and  it  is  to  be  expected  that  the  statistics  for  1909  will  show  a 
decided  increase.  The  above  table  represents  the  report  of 
some  471  producers. 

The  following  tables,  compiled  by  Parker,*  show  the  produc- 
tion and  value  of  coal  tar  and  water  gas  and  oil  tars  for  1907 
and  1908  by  states. 

The  chemical  and  physical  characteristics  of  tars  relative  to 
their  use  as  dust  preventives  and  road  binders  require  fully  as 
much  study  as  do  the  oils.  As  shown  by  the  foregoing  tables, 
this  class  of  materials  offers  a  very  large  source  of  supply  and  in 
the  author's  opinion  a  very  valuable  one.  The  value  of  tar  for 
street  paving  work  has  been  much  belittled  by  those  interested 
in  the  asphalt  industry  and  because  of  their  activities  it  has 
fallen  into  general  disrepute,  so  much  so  as  to  be  considered  one 
of  the  worst  of  all  adulterants.  As  a  result  of  this  it  will  un- 
doubtedly take  some  time  for  tars  to  assume  their  rightful 
position  in  the  eyes  of  the  public,  but  the  recent  development 
of  the  bituminous  road  material  industries,  in  which  they  are  an 
important  factor,  is  gradually  accomplishing  this  result.  ( Had 
[tars  received  as  much  study  as  oils  and  asphalts  from  the 
standpoint  of  paving,  they  would  have  been  on  a  better  footing 
[long  before  now.)  The  methods  of  tar  manufacture  and  a  con- 
sideration ot  the  characteristics  possessed  by  different  kinds  of 
tars  and  their  various  constituents  cover  an  immense  field  and 
volumes  have  been  written  upon  only  small  portions  of  the 
subject.  It  is  evidently  impossible,  therefore,  in  a  single  chap- 
ter to  give  more  than  a  brief  outline  of  the  subject  and  point 
out  in  a  general  way  the  relations  between  certain  properties 
of  the  materials  and  the  results  obtained  by  their  use  as  dust 
preventives  and  road  binders. 

*  "  Mineral  Resources  of  the  United  States,  Calendar  Year  1908."  U.  S.  Geo- 
logical Survey. 


TAR   AND   TAR   PRODUCTS 


231 


RANK  OF  STATES  IN  COAL  TAR  PRODUCTION  IN  1907  AND   1908. 

1907. 


J4 

3 

& 

State. 

Num- 
ber of 
Estab- 
lish- 
ments. 

Quantity. 

Value. 

Value 
per 
Gallon 

Yield 
per  Ton 
of  Coal. 

i 

Pennsylvania                           .  . 

28 

Gallons. 
18,304,661 

$412,127 

Cents. 
2  .  3 

Gallons 
6.34 

2 

New  York 

CO 

13,760.436 

302,200 

2.  2 

0.^8 

Massachusetts          

41 

10,650,702 

299,219 

2.8 

10.  72 

4 

Ohio                         

32 

8,O95,3OC, 

218,986 

2  .  7 

11.23 

C 

Michigan  

44 

8,038,584 

173,599 

2  .  2 

10.86 

1 

Illinois   

4° 

6,383,121; 

125,049 

2  .O 

8.40 

7 

Alabama  

ii 

5,898,064 

177,879 

3.O 

8.31 

8 

Wisconsin  

21 

5,436,098 

129,556 

2.4 

7.70 

9 
10 

Delaware,  District  of  Colum- 
bia, and  Maryland    
New  Jersey 

10 
ir 

4,208,105 

3,073,2^1 

86,445 
121,049 

2.  I 
3     I 

8.12 
940 

1  1 

Missouri 

14 

3,870,388 

QO,4?2 

2    3 

10  63 

12 
I  3 

Virginia  and  West  Virginia.  . 
Minnesota     

16 

8 

3.094,593 
2,388,283 

93,558 
70,082 

3-o 

2.O 

.ly.u^ 
16.95 

ii  88 

14 

Indiana      

20 

1,408,434 

36,040 

2    4 

10.  7i 

3 

Kentucky  
Connecticut  

II 

7 

976,622 

886,3^0 

22,577 
32,114 

5:i 

9.98 

12  .OQ 

17 

Colorado  

7 

861,700 

40,700 

4.  7 

II  .  62 

18 

Iowa 

18 

7^0  31  7 

18  906 

2     C 

10  98 

10 

Tennessee 

7 

7^.4  1  3£. 

27233 

•  •  0 
3    6 

II     31 

20 

Rhode  Island 

644  026 

I  7  r  36 

2    7 

II     33 

21 

Georgia                      

g 

63  c  880 

18  738 

2    o 

Q    48 

22 
23 

Washington  
Maine  

9 

7 

634,491 

2QC  O34 

44,804 
1  1   34Q 

7-i 

3    8 

10.91 
14    ^4 

24 

North    Carolina    and    South 
Carolina  

7 

2QI.87I 

1  1  7Q2 

40 

IO    C.  3 

25 

"6 

New  Hampshire  and  Vermont 
Texas 

5 

7 

235,324 
22C   3QA 

11,388 
12  7O7 

4.8 
t  6 

11.94 

7    O7 

27 

Oklahoma     

IQ3   £.31 

14  27C. 

c>  •  u 
7   4 

8  s6 

28 
29 

Idaho,   Montana,  North  Da- 
kota, and  Wyoming  
Nevada,    New    Mexico,    and 
Utah  

6 
4 

144,411 
I2O  O2  £ 

9,831 
7  431 

6.8 
6  i 

9-93 

IO    2  C 

30 
31 

Kansas  and  Nebraska  
Florida,  Louisiana,  and  Mis- 
sissippi   

5 

7 

113,522 

nr  87O 

4,082 

•2   QC  (• 

3-6 

7-99 
10  60 

32 

Arkansas  

7  1  7OO 

O'VOJ 

3771 

5-3 

ii   38 

-}-} 

Oregon  

3 

IQ  42  I 

i  008 

•6 
IO    3 

13    17 

j.u.  ^ 

488 

I03,577,760 

2,651,527 

2.6 

9.04 

232 


DUST   PREVENTIVES    AND    ROAD  BINDERS 


RANK  OF  STATES  IN  COAL  TAR  PRODUCTION  IN  1908. 


1 

State. 

Num- 
ber of 
Estab- 
lish- 
ments. 

Quantity. 

Value. 

Value 
per 
Gallon. 

Yield 
per  Ton 
of  Coal. 

I 

Pennsylvania            

25 

18,720,845 

$401  0^2 

2     I 

10  76 

2 

New  York             

48 

14,688,070 

•3  I?    664 

2     I 

IO    33 

•$ 

Massachusetts  

78 

10,493,400 

284,664 

2     7 

10  6< 

4 

Michigan  

42 

7,834,7^7 

182X71 

2    3 

II      AC 

c 

Ohio 

27 

6  774.  IQ3 

192    682 

2    8 

12     32 

6 

Illinois 

4? 

6  248  601; 

I4O  IQO 

2    2 

8    13 

7 

Alabama 

1  1 

6  24.4  4QI 

I  76  8<4 

2    8 

8  62 

8 

Wisconsin 

18 

C,CC7  r-?7 

I  -1  £    71  1 

2    4 

8  oi 

9 

Delaware,  District  of  Colum- 
bia, and  Maryland    

1  1 

4,120  124 

QI,8o4 

2    2 

927 

10 

New  Jersey  

I  3 

4,127,126 

123,662 

3O 

0     ^2 

ii 

Missouri      

I  £ 

3,874,4^4 

8Q,4O3 

2     3 

7      J 

21  .  OO 

12 

Minnesota  

2,3QI,667 

6l,677 

2.6 

11.88 

T3 

Indiana  

3O 

I,q87,8l7 

4O,  T.QZ 

2  .  ? 

10.  76 

14 

Kentucky 

I   3Q7  4Q2 

29  676 

2     I 

1  3    30 

it; 

Colorado 

6 

Q26  OQ4 

42  62  I 

4    6 

9    O2 

16 

17 

Virginia  and  West  Virginia.  . 
Connecticut     

15 

6 

924,805 
8lQ  317 

24,5°3 

29  01  1 

2.6 

•2      f 

10.92 
IO    62 

78 

Washington  

668  oo  q 

•36,20? 

r    4 

IO  .  14 

I9 

Iowa       

16 

6s8,4(C4 

18,444 

o  8 

8.82 

20 

Tennessee    

7 

646,760 

24,422 

3.8 

0.43 

?T 

Rhode  Island  

3 

628,968 

16,843 

2  .  7 

ii.  8c 

22 

Georgia 

2QO  424. 

1  1  O2I 

3    7 

414 

2^ 

M^aine 

278  io<; 

IO  I2O 

3    6 

1  3    36 

24 

New  Mexico,  Oklahoma,  and 
Utah       .            

6 

264,209 

7,731 

2    0 

IO.  2O 

25 

North    Carolina    and    South 
Carolina  

8 

2?3,?2O 

10,467 

4  •  i 

8.56 

26 

?7 

New  Hampshire  and  Vermont 
Kansas  and  Nebraska  

6 
6 

238,847 
202,384 

12,076 
e,6i7 

5-o 

2.8 

10.78 
I5.O3 

28 

Idaho,  Montana,  North  Da- 
kota,   South    Dakota,    and 
WVoming  

7 

128,170 

8,4<^ 

6.6 

8.40 

20 

Texas     

6 

101,580 

5,788 

c.7 

4.  63 

3° 

Florida,  Louisiana,  and  Mis- 
sissippi 

6 

70,1  IO 

4,244 

e   4 

8.  74 

71 

Arkansas 

65,200 

2,026 

4.  ir 

II   .OI 

32 

California  and  Oregon  

•3 

Q.2OO 

Q2O 

IO.O 

^  -41 

471 

IOI,26l,829 

2,537>u8 

2-5 

10.30 

TAR   AND   TAR   PRODUCTS 


233 


QUANTITY  AND  VALUE  OF  TAR  PRODUCED  AND  SOLD  AT  WATER 
GAS  AND  OIL  GAS  WORKS  IN  THE  UNITED  STATES  IN  1907  AND 
1908. 

1907. 


State. 

Total 

Quantity. 

Total 

Value. 

Price  per 
Gallon. 

Arkansas,  Florida,  Louisiana,  and  Mississippi... 
California  and  Washington  

Gallons. 
440,563 
3,388,801 

$I3»396 
78,^1:4 

Cents 

3-° 
2  .  3 

Connecticut  and  Massachusetts  

2,142,476 

^8,914 

2  .  7 

Delaware,  Maryland,  and  New  Jersey  

1,871,500 

4tj,8e.o 

2  .4 

Georgia  and  South  Carolina 

•2  A    4  -2Q 

2   262 

6  6 

Illinois    Indiana    and  Ohio 

132    3OO 

2  67< 

2    O 

Iowa 

204,l82 

7,O3I 

2    4 

Minnesota  and  Wisconsin        .                               .  . 

664,4^7 

2I,6OO 

3    2 

Nebraska  and  South  Dakota               

4=54,314 

II,2O5 

2    4 

Missouri                 

3,oc.o 

163 

e  .  3 

New  Hampshire    

58,120 

777 

1  .  3 

New  York  

3,619,788 

72,626 

2  .O 

Pennsylvania 

I   2O7   I  ^6 

24  i  C.2 

2    O 

Texas 

IO2   781 

2  737 

2     7 

14,414,017 

342,041 

2.4 

1908. 

California  and  Washington 

724,031 

3C.  471 

4Q 

Connecticut,  Massachusetts,  and  New  Hampshire 
Delaware  and  Maryland           

2,364,190 
1  37,917 

58>54Q 
2,072 

2-5 

I     C. 

Florida,  Louisiana,  Mississippi,  and  Texas  

^8,714 

is,  207 

2     7 

Georgia  and  South  Carolina 

22  8OO 

i  061 

47 

Illinois 

2  1  ,  6OO 

C.24 

2    4 

Indiana  and  Ohio 

^7,322 

12,360 

2    2 

Iowa                                                                         .    .  . 

361,760 

7  roC 

2     I 

Michigan,  Minnesota,  and  Wisconsin  
Missouri,  Nebraska,  and  South  Dakota  
New  Jersey                                                              t 

6i5>°55 
458,637 

114  QOO 

/o'o 

19,316 

i°>357 
i  8oe, 

3-i 

1:1 

New  York 

2,804.  727 

58,620 

2    O 

Pennsylvania.  .                              

^7,l8l 

6,744 

2    o 

*9,  1  68,834 

229,582 

2-5 

*  In  addition  5,559,199  gallons  were  reported  as  produced  but  not  sold. 


234 


DUST  PREVENTIVES   AND  ROAD   BINDERS 


Gas  House  Coal  Tars.  —  Gas  house  coal  tar  is  a  by-product 
obtained  in  the  manufacture  of  illuminating  gas  from  coal. 
In  the  early  days  of  manufacture  it  was  considered  a  waste 
product  having  no  value,  and  often  proved  a  great  nuisance  to 
gas  producers,  who  we,re  at  a  loss  to  know  how  to  dispose  of  it 
in  a  sanitary  manner.  Because  of  the  great  number  of  hydro- 
carbons which  it  contains  it  offered  an  inexhaustible  field  of 
research  to  many  chemists  and  as  a  result  of  their  investiga- 
tions, great  industries  have  sprung  into  existence  whose  basis 
of  operation  lies  in  the  synthetic  preparation  of  many  valuable 
products  hitherto  unknown,  or  obtainable  only  at  great  expense 
from  a  few  natural  sources. 

In  the  manufacture  of  illuminating  gas,  bituminous  coal  is 
placed  in  Q  shaped  fire  clay  retorts  about  8  feet  long,  15 
inches  high  and  18  inches  wide.  Six  or  eight  of  these  retorts 
are  set  together  in  a  furnace  and  constitute  what  is  commonly 
known  as  a  bench.  A  number  of  these  benches  built  together 
is  called  a  stack.  The  retorts  are  usually  set  horizontally  or 
at  just  sufficient  angle  to  allow  of  their  being  discharged  easily, 
and  are  heated  by  means  of  a  coke  fire  or  by  generator  gas. 
Fig.  21  shows  the  most  important  parts  of  the  process  in  detail. 


D 

B 

vy~to 

E 

S 

^                i, 

P        A        J 

[f      u 

_n 


FIG.  21.     Sketch  Illustrating  the  Production  of  Tar  in  the  Manufacture  of 

Coal  Gas. 

Before  the  coal  is  heated  all  of  the  openings  in  each  retort  A 
are  closed  with  the  exception  of  a  vertical  pipe  extending  up- 
wards from  the  front.  The  volatile  products  from  the  heated 
coal  pass  up  this  stand-pipe  B  which  connects  with  the  bridge 
C  and  the  dip  pipe  D  and  are  thus  conducted  to  a  long  covered 


TAR  AND   TAR   PRODUCTS  235 

trough  running  the  whole  length  of  the  stack  and  known  as  the 
hydraulic  main  E,  in  which  the  greater  part  of  the  tarry  products 
condense  and  collect  under  water,  which  is  kept  in  the  main  to 
act  as  a  seal  and  also  to  dissolve  the  ammonium  salts  which  are 
formed.  As  the  tar  collects  it  is  drawn  off  by  various  ingenious 
devices  upon  reaching  a  certain  height  in  the  hydraulic  main. 
The  gas  now  passes  from  the  main  to  the  condensing  plant  JF, 
which  usually  consists  of  a  series  of  vertical  cast  iron  pipes 
connected  at  the  top  and  opening  at  the  bottom  into  an  iron 
box  which  is  divided  by  transverse  partitions,  extending  nearly 
to  the  bottom  and  dipping  into  the  condensed  products  so  that 
the  gas  is  forced  to  pass  through  the  pipes.  The  condenser  is 
cooled  either  by  air  or  water  in  such  a  manner  that  the  gas  is 
brought  slowly  to  a  temperature  of  about  50°  C.  Tar  and 
ammoniacal  liquor  are  condensed  here  and  flow  from  the  box 
into  a  storage  well.  A  mechanical  device  known  as  the  ex- 
hauster G  draws  the  gas  from  the  condenser  and  forces  it  through 
the  remaining  parts  of  the  plant.  From  the  exhauster  the  gas 
passes  into  a  tower  fitted  with  numerous  horizontal  perforated 
plates  called  the  tar  extractor  H,  where  the  friction  of  the  gas 
in  passing  through  the  perforations  removes  the  last  traces  of 
tar.  From  this  point  on  the  process  of  gas  manufacture  ceases 
to  be  of  interest  in  relation  to  the  production  of  tar  and  it  is 
only  necessary  to  add  that  before  the  gas  can  be  used  for  illu- 
minating purposes  it  has  to  be  further  purified  by  passing  it 
through  scrubbers,  washers  and  purifiers  of  different  kinds  in 
order  to  remove  the  remaining  ammonia,  carbon  dioxide,  hydro- 
gen sulphide  and  other  sulphur  compounds  formed.  The  non- 
volatile part  of  the  coal  remains  in  the  retort  as  coke.  The 
tar  from  the  hydraulic  main  is  thicker  than  that  obtained  from 
the  condensers  and  scrubbers  and  poorer  in  volatile  products. 
It  represents  about  62  per  cent  of  the  entire  amount,  while  that 
from  the  condensers  amounts  to  nearly  12  per  cent  and  that 
from  the  scrubbers  about  26  per  cent.  All  of  the  tar  is  run 
together  into  large  wells,  where  it  is  allowed  to  settle  for  some 
time  in  order  to  separate  it  as  far  as  possible  from  the  ammoniacal 


236  DUST  PREVENTIVES  AND   ROAD   BINDERS 

liquor  present.  This  ammoniacal  liquor  being  lighter  than  the 
tar  rises  to  the  top  and  is  drawn  off  for  use  in  the  manufacture 
of  ammonia. 

The  crude  coal  tar  which  remains  is  a  black  more  or  less 
viscid  fluid  of  peculiar  smell  and  varying  in  specific  gravity 
from  i.io  to  1.25  and  sometimes  higher.  As  has  been  stated, 
it  is  an  exceedingly  complex  mixture  of  chemical  compounds 
and  always  contains  a  certain  amount  of  ammoniacal  liquor  as 
well  as  several  constituents  of  the  illuminating  gas  in  solution. 

While  the  character  of  the  coal  will  have  considerable  effect 
upon  that  of  the  tar  produced,  the  temperature  at  which  the 
retort  is  fired  is  also  a  most  important  modifying  factor,  as  will 
be  shown  later.  The  temperature  of  the  retort  varies  in 
different  gas  works  from  between  850°  and  970°  C.,  known  as 
low  temperature,  to  between  1100°  and  1540°  C.,  known  as  high 
temperature.  From  970°  to  nooc  C.  is  considered  medium 
temperature.  The  temperature  of  the  coal  is  somewhat  lower 
than  that  of  the  retort,  especially  at  the  center  of  the  charge. 
The  yield  of  tar  per  ton  of  coal  will  vary  from  about  8  gallons 
when  high  temperatures  are  employed  to  as  much  as  16  gallons 
at  medium  and  low  temperatures.  The  maximum  variation  as 
shown  by  the  tables  of  coal  tar  production  is  from  4.  i  gallons 
to  21.6  gallons.  Other  things  being  equal,  the  amount  of  gas 
produced  increases  with  the  temperature.  In  gas  plants  an 
attempt  is  made  to  get  as  much  gas  as  possible  out  of  the  coal 
and,  therefore,  to  distill  at  the  highest  possible  temperature. 
Up  to  a  certain  point,  this  is  quite  rational,  but  beyond  it 
modifying  factors  have  to  be  considered.  While  the  quantity 
of  gas  increases  with  the  temperature,  its  illuminating  power 
diminishes.  This  is  due  to  the  tendency  displayed  by  the 
hydrocarbons  to  dissociate  at  high  temperatures  into  their  ele- 
ments, hydrogen  and  carbon.  Thus  hydrogen  will  be  produced 
as  a  gas  and  free  carbon  will  be  deposited  in  the  tarry  con- 
densations, also  the  proportion  of  such  substances  as  naphtha- 
lene and  anthracene  will  be  increased  in  the  tar.  If  the  higher 
temperatures  are  employed  it  will  become  necessary  to  enrich 


TAR   AND   TAR   PRODUCTS 


237 


the  gas  by  the  addition  of  oil  products  in  order  to  give  it 
the  proper  illuminating  value.  In  cases  where  the  enriching 
oil  is  cheap,  the  method  is  often  employed,  while  in  others  it 
is  considered  more  economical  to  produce  a  smaller  amount  of 
gas  from  the  coal,  which  shall  be  richer  in  illuminants.  The 
results  of  the  examination  of  two  crude  coal  tars,  one  produced 
at  medium  and  the  other  at  high  temperature,  are  given  in  the 
following  table: 

CRUDE    GAS    HOUSE  TARS. 


Type    ...              

(0 

Medium 

(•) 

High 

Temperature 

Temperature 

Character 

Viscous 

Viscous, 

Specific  gravity,  2$°/2$°  C  

Fairly  smooth 
1.188 

Lumpy 

I  .  2<O 

Distillation  

Ammoniacal  water,  per  cent  by  vol  

o.  3 

4.O 

First  light  oils  to  110°  C.,  per  cent  by  vol  

4-4 

2  .  ? 

Second  light  oils  no°-i7o°C.,  per  cent  by  vol.  ... 
Heavy  oils  170°—  270°  C  ,  per  cent  by  vol 

16.5 

•y-i    e 

!7-5 

1  7  .  0 

Pitch  residue  (by  difference),  per  cent  by  vol 

4.r  .  -2 

CQ.O 

Pitch  residue,  per  cent  by  weight  

100.  0 

cc  .  7 

100.  0 

67.1 

Free  carbon  (insoluble  in  CS2)  

20.89 

30.90 

Remarks.  —  In  tar  No.  i  the  second  light  oil  distillate  showed  about  two-thiids 
of  its  volume  precipitated  naphthalene  when  cold,  and  the  heavy  oil  distillate 
about  two-fifths  of  its  volume  precipitated  naphthalene.  In  tar  No.  2  both 
the  second  light  and  heavy  oils  were  nearly  solid  naphthalene  when  cold. 
The  pitch  residue  of  No.  i  showed  a  fairly  lustrous  fracture,  while  the  frac- 
ture of  No.  2  was  dull. 

A  comparison  of  these  two  tars  shows  the  effect  of  high  tem- 
peratures in  an  increase  in  specific  gravity  directly  attribu- 
table to  the  increase  in  free  carbon,  an  increase  in  pitch  residue, 
and  a  decrease  in  the  heavy  or  dead  oils.  The  presence  of 
ammoniacal  water  and  oils  distilling  below  no°C.  is  the  dis- 
tinguishing feature  of  all  crude  coal  tars.  Any  amount  of  the 
former  makes  the  tar  unsatisfactory  for  road  purposes,  both  be- 
cause of  the  saponifying  action  of  the  ammonia  and  because 
water  prevents  proper  absorption  by  and  adhesion  to  the  road 


238  DUST   PREVENTIVES    AND    ROAD    BINDERS 

material.  Tar  No.  i  runs  exceptionally  low  in  this  constituent 
and  probably  represents  a  sample  which  has  been  taken  from 
near  the  bottom  of  the  well  after  settling  for  a  long  time.  It 
might  be  employed  to  some  advantage  in  the  surface  treat- 
ment of  a  macadam  road  as  a  dust  preventive  and  semiperma- 
nent binder,  but  would  have  to  be  applied  hot.  Tar  No.  2  is 
in  its  natural  condition  unsuited  for  road  work  both  because  of 
the  presence  of  water  and  its  high  naphthalene  and  free  carbon 
content.  As  will  appear  later,  neither  tar  is  capable  of  being 
refined  to  make  a  good  road  binder  unless  blended  with  another 
tar  having  quite  different  characteristics.  While  crude  tars 
are  quite  viscous,  they  sweat  badly  under  the  action  of  sun  and 
traffic  after  being  applied  to  the  road,  and  have  not  sufficient 
body  to  be  employed  in  construction  work.  The  lumpy  ap- 
pearance of  No.  2  is  due  to  the  presence  of  an  excess  of  free 
carbon,  which  gives  the  bitumen  a  false  consistency.  The  light 
oils  can  only  be  considered  as  volatile  diluents,  of  no  value 
for  road  purposes,  although  from  the  tar  refiner's  point  of  view 
they  may  be  the  most  valuable  constituent.  The  heavy  oils 
are  of  service  in  keeping  the  tar  from  becoming  too  brittle  after 
the  lighter  oils  have  evaporated,  providing  that  they  are  not 
composed  mainly  of  naphthalene,  as  in  the  case  of  No.  2.  The 
true  binding  base  of  the  tar  is  present  in  the  pitch  residue, 
although  in  order  that  it  may  be  developed  properly,  it  is 
necessary  for  it  to  be  fluxed  with  heavy  oils.  While  No.  2  has 
apparently  a  much  greater  per  cent  of  this  binding  base  than 
No.  i,  as  shown  by  the  relative  amount  of  pitch  residue,  it 
should  be  remembered  that  these  residues  contain  free  carbon 
which,  as  will  be  shown  later,  has  no  binding  value.  If  the  per- 
centage of  free  carbon  be  subtracted  in  each  case  from  the  per 
cent  of  pitch  by  weight,  it  will  be  seen  that  there  is  very  little 
difference  between  the  two  tars  in  the  actual  amount  of  bitumen 
present  in  the  residues.  Thus  No.  i  would  show  34.81  per 
cent  and  No.  2,  36.20,  giving  a  difference  of  less  than  2  per 
cent.  While  this  would  seem  to  be  a  slight  advantage  in 
favor  of  No.  2,  it  is  not  in  reality,  because  of  the  proportion- 


TAR   AND   TAR   PRODUCTS  239 

ately  small  amount  and  inferior  character  of  the  heavy  oils 
wnich  are  necessary  to  keep  life  in  the  tar. 

Coke  Oven  Tars.  —  While  in  the  manufacture  of  coal  gas  the 
production  of  tar  is  absolutely  unavoidable,  this  is  not  true  of 
the  manufacture  of  coke  for  metallurgical  purposes.  There  are 
two  general  types  of  coke  ovens  in  use  at  present,  in  one  of 
which  no  attempt  is  made  to  recover  the  volatile  products  of 
the  coal.  This  is  the  oldest  form  of  oven,  known  as  "the  bee- 
hive," and  is  extensively  used  in  this  country  to-day.  It  is 
constructed  of  brick  and  as  its  name  implies  has  the  form  of  a 
beehive.  Bituminous  coal  is  placed  in  this  oven  or  kiln  and  a 
part  of  it  burned  in  order  to  carbonize  the  remainder,  while  the 
volatile  products,  such  as  gas,  ammonia,  and  tar,  are  allowed  to 
escape  through  an  opening  in  the  top  of  the  kiln  where  they 
are  lost  in  flame  and  smoke. 

Coke  ovens  in  which  the  by-products  are  saved  are  now  used 
to  some  extent  in  this  country  and  sooner  or  later  will  undoubt- 
edly replace  the  old  style  oven  entirely,  and  thus '  enormously 
increase  our  output  of  tar.  The  reason  that  they  have  not 
been  more  generally  adopted  in  this  country  is  that  in  the 
United  States  tars  are  of  much  less  economic  importance  than 
in  the  European  countries,  where  great  chemical  industries  are 
based  upon  the  utilization  of  this  material.  Germany  in  par- 
ticular is  far  in  advance  of  us  in  this  field  and  exports  to  this 
country  alone  coal  tar  products  to  the  value  of  several  million 
dollars  each  year.  With  the  development  of  the  road  tar 
industry,  which  promises  to  consume  vast  quantities  of  tar,  and 
the  necessity  for  refining  such  tars  before  use,  the  general 
adoption  of  by-product  ovens  is  only  a  matter  of  time.  What 
this  will  mean  in  the  increase  in  tar  production  can  be  imagined 
from  the  fact  that  in  1908,  out  of  a  total  of  over  26  million  tons 
of  coke  produced  in  coke  ovens,  only  a  little  over  4  million  tons 
were  obtained  from  by-product  ovens.  About  22  million  tons  of 
coke  were,  therefore,  produced  without  recovery  of  the  tar.  As 
the  average  yield  of  coke  per  ton  of  coal  was  66  per  cent,  this 
would  represent  the  consumption  of  over  33  million  tons  of 


240  DUST  PREVENTIVES   AND    ROAD   BINDERS 

coal.  Upon  the  basis  of  a  yield  of  10  gallons  of  tar  per  ton  of 
coal,  it  may  be  seen  that  over  330  million  gallons  of  tar  were 
lost  which  might  have  been  saved  in  1908.  As  the  actual  pro- 
duction of  coal  tar  both  from  coke  ovens  and  gas  houses 
amounted  to  about  101  million  gallons,  it  is  evident  that  over 
three-fourths  of  our  possible  production  of  tar  as  a  by-product 
was  lost  during  that  year.  At  a  valuation  of  two  and  one-half 
cents  per  gallon,  this  means  a  loss  of  over  8  million  dollars. 
With  such  an  increase  in  production,  however,  the  monetary 
value  of  coal  tar  would  have  dropped,  so  that  this  figure  may  be 
somewhat  exaggerated.  In  any  event  at  a  conservative  esti- 
mate the  tar  lost  each  year  from  non-recovery  coke  ovens  is 
sufficient  to  build  9,000  miles  of  tar  macadam  road,  15  feet  wide. 
There  are  several  kinds  of  by-product  coke  ovens  now  in  use, 
the  most  common  being  the  Coppee,  the  Otto-Hoffmann,  the 
Simon-Carves  and  the  Semet-Solvay.  In  these  a  coke  suitable 
for  metallurgical  purposes  is  produced,  and  the  ammonia  and 
coal  tar  recovered.  Whichever  oven  is  employed  the  method  is 
entirely  analogous  to  gas  manufacture,  and  stripped  of  all 
details  is  conducted  as  follows:  The  coal  is  charged  into  long, 
narrow  chambers  or  retorts  of  from  4  to  6  tons  capacity,  heated 
by  means  of  flues  set  in  the  retort  walls.  The  volatile  portions  of 
the  coal  pass  out  through  an  opening  in  the  top  to  the  hydraulic 
main  and  are  thence  conducted  through  a  series  of  washers  and 
scrubbers,  as  in  the  manufacture  of  gas,  in  order  to  remove  the 
tar  and  ammonia.  The  purified  gas  is  then  allowed  to  pass  into 
a  holder  from  which  it  is  drawn  as  needed  for  burning  under  the 
retorts.  As  the  object  of  the  coke  manufacturer  is  to  obtain 
the  largest  possible  yield  of  coke  from  his  coal,  and  as  the  quan- 
tity of  gas  produced  is  only  a  secondary  consideration,  he 
usually  fires  his  retort  at  a  comparatively  low  temperature,  not 
much  in  excess  of  1000°  C.  and  sometimes  considerably  lower. 
This  results  in  an  increase  in  the  yield  of  tar  over  that  of  mod- 
ern gas  manufacture  and  incidentally  in  an  improvement  in 
the  quality  of  the  tar  for  road  purposes,  as  can  be  seen  from  the 
results  of  examination  of  two  typical  American  coke  oven  tars 


TAR   AND   TAR  PRODUCTS 


241 


given  below.  It  should  be  mentioned,  however,  that  some  coke 
ovens,  particularly  the  Otto,  are  fired  at  higher  temperatures  and 
produce  tars  quite  similar  to  gas  house  coal  tars. 

CRUDE    COKE    OVEN    TARS. 


(0 

(a) 

Character            ... 

Viscous, 

Viscous, 

Specific  gravity    2$°/2$°  C 

Smooth 
i  162 

Smooth 
i  .  167 

Distillation: 
Ammoniacal  water,  per  cent  by  vol 

2    O 

i  .0 

First  light  oils  to  no0  C.,  per  cent  by  vol  
Second  light  oils,  iio°-i7o°  C.,  per  cent  by  vol..  .  . 
Heavy  oils,  170°—  270°  C.,  per  cent  by  vol  

2.8 

15-9 

•21  .  £ 

I.O 

6.0 

32.8 

Pitch  residue  (by  difference),  per  cent  by  vol  

47.8 

59-2 

Pitch  residue,  per  cent  by  weight 

IOO.O 
^2    4. 

IOO.O 

64.  7 

Free  carbon  (insoluble  in  CS?)..                  

6.7O% 

8.56% 

Remarks.  —  In  tar  No.  i  the  second  light  oil  distillate  showed  only  a  trace  of 
precipitated  naphthalene  when  cold  and  the  heavy  oil  distillate  about  one- 
half  its  volume  precipitated  naphthalene.  In  tar  No.  2  the  second  light  oils 
solidified  when  cold  and  the  heavy  oil  distillate  showed  about  one-half  its 
volume  precipitated  naphthalene.  The  pitch  residues  from  both  showed  a 
fairly  lustrous  fracture- 

The  two  tars  shown  above  were  produced  at  comparatively 
low  temperatures,  as  evidenced  by  their  low  free  carbon  content 
and  rather  low  specific  gravity.  As  in  the  case  of  crude  gas 
house  coal  tars  they  contain  ammoniacal  water  and  light  oils 
distilling  below  no°C.  While  both  of  these  tars  show  con- 
siderable quantities  of  naphthalene,  the  heavy  oil  fraction  is 
large  as  in  the  case  of  the  medium  temperature  crude  gas  house 
coal  tar,  so  that  a  considerable  amount  of  heavy  fluid  distillate 
is  present.  After  deducting  the  free  carbon,  they  both  show 
higher  percentages  of  pitch  bitumens  than  do  either  of  the  gas 
house  tars  previously  described.  This  is  characteristic  of  low 
temperature  tars  and  constitutes  one  of  their  chief  advantages. 
Both  of  these  materials  could  be  refined  to  produce  good  binders 
for  macadam  road  construction,  as  will  be  shown  later.  The  low 
percentage  of  free  carbon  is  characteristic  of  the  Semet-Solvay 
coke  oven  tars,  which  usually  carry  from  3  to  10  per  cent  of 


242  DUST   PREVENTIVES  AND    ROAD   BINDERS 

this  constituent.  The  Otto-Hoffmann  ovens  produce  higher 
carbon  tars  as  they  are  fired  at  a  higher  temperature. 

Theory  of  Formation  of  Coal  Tar  Hydrocarbons.  —  The 
formation  of  coal  tar  hydrocarbons  is  an  extremely  compli- 
cated subject  and  a  number  of  theories  have  been  advanced  by 
eminent  chemists,  none  of  which  is  entirely  satisfactory.  So 
many  modifying  factors  have  to  be  considered  that  it  is  doubt- 
ful if  any  one  theory  will  ever  be  found  to  cover  them  all.  In  a 
book  of  this  nature  it  is  unnecessary  to  enter  into  a  detailed 
discussion  of  these  theories,  but  some  of  the  most  important 
should  be  briefly  reviewed  in  order  to  give  some  idea  of  the 
differences  in  character  of  the  various  coal  tars. 

Besides  the  character  of  the  coal  itself,  there  are  at  least 
three  important  factors  which  affect  the  products  of  the  de- 
structive distillation  of  coal.  They  are  time,  temperature  and 
pressure. 

Little  is  known  of  the  molecular  composition  of  coals,  al- 
though their  ultimate  composition  has  been  determined  in 
many  instances  and  found  to  vary  greatly  in  different  samples. 
While  coal  is  sometimes  considered  as  a  complex  molecule,  it  is 
in  all  probability  a  complex  mixture  and  the  composition  of  the 
tar  which  it  produces  must  necessarily  vary  with  the  character 
and  relative  proportions  of  the  compounds  which  it  contains 
and,  therefore,  with  the  ratio  of  hydrogen,  carbon,  oxygen,  etc., 
to  one  another.  It  is  definitely  known  that  tar  is  not  a  simple 
mixture  of  the  volatile  constituents  of  the  coal,  but  that  it  is 
the  product  of  complex  chemical  reactions  which  take  place 
during  the  process  of  carbonization.  All  chemical  reactions  are 
influenced  by  time,  temperature  and  pressure  and  the  forma- 
tion of  coal  tar  must,  therefore,  be  influenced  by  these  factors. 
As  an  actual  example  of  the  effect  of  temperature,  reference  may 
be  made  to  a  statement  by  Jayne:*  "The  influence  of  the 
temperature  used  in  carbonizing  is  strikingly  shown  by  the  test 
of  two  tars,  both  from  the  same  coal,  and  made  in  the  same 

*  "The  Coal  Tar  Industry  in  the  United  States."  Paper  presented  to  the 
Fourth  International  Congress  of  Applied  Chemistry,  June,  1903. 


TAR   AND   TAR   PRODUCTS  243 

kind  of  ovens.  One  plant  was  producing  gas  as  its  main  object. 
The  tar  from  this  plant  had  a  gravity  of  1.21  and  tested  17.5 
per  cent  of  carbon;  the  light  oil  fraction  was  2.2  per  cent  of  a 
gravity  0.979,  testing  23  per  cent  to  170  degrees;  the  total  acids  in 
the  tar  oils  were  3.6  per  cent  and  the  dry  pressed  naphthalene  7.4 
per  cent.  In  the  second  tar,  in  which  coke  was  the  main  object, 
evidently  much  lower  heats  were  used,  the  tar  having  a  gravity 
of  1.137  and  testing  3.2  per  cent  of  carbon;  the  light  oil  amounted 
to  11.9  per  cent,  and  had  a  gravity  of  0.970,  testing  28  per 
cent  to  170  degrees,  or  six  times  more  crude  naphtha  than  in 
first  tar;  the  total  tar  acids  were  12.48  per  cent  while  the  pressed 
naphthalene  fell  to  1.2  per  cent.  It  is  evident  that  in  the  first 
tar  the  light  hydrocarbons  and  tar  acids  have  been  destroyed 
by  the  temperature  employed  with  the  formation  of  naphtha- 
lene." 

The  probable  character  of  the  reactions  which -take  place  in 
the  retort  have  been  very  clearly  stated  by  Fulweiler*  as  fol- 
lows: "The  carbonization  of  coal  in  any  retort  proceeds  in 
three  general  stages: 

"First. — There  is  a  preliminary  decomposition,  which  begins 
as  soon  as  the  coal  has  acquired  a  certain  fairly  definite  temper- 
ature, and  as  this  stage  is  quite  strongly  endothermic,  approach- 
ing as  it  does  a  fusion,  the  temperature  remains  practically 
constant  until  completion. 

"Second. — The  products  resulting  from  the  first  stage, 
which  consist  principally  of  the  higher  members  of  the  chain, 
or  aliphatic  series,  suffer  very  considerable  molecular  rear- 
rangement. In  general,  since  the  C— H  bond  seems  stronger 
than  the  C— C  bond,  compounds  containing  less  than  three 
atoms  of  carbon  are  formed.  This  stage  may  be  looked  upon 
as  a  continuance  of  the  simplification  in  which  every  distilla- 
tion results. 

"These  first  two  stages  take  place  almost  simultaneously 
within  the  charge  itself  and  are  both  endothermic. 

*  "  The  Physical  Theory  of  Coal  Carbonization."  Paper  written  for  the  Third 
Annual  Meeting  of  the  American  Gas  Institute. 


244  °UST   PREVENTIVES   AND    ROAD   BINDERS 

"  Third.  —  The  gaseous  vapors  resulting  from  the  second 
stage,  when  evolved  from  the  protecting  influence  of  the  actual 
coal  particles,  are  acted  upon  by  the  conducted  and  radiant 
heat  of  the  more  highly  heated  portions  of  the  charge  proper,  of 
the  sides  of  the  containing  retort  and  of  the  superheated  sur- 
faces above  the  coal  (or  free  space). 

"The  reactions  taking  place  at  this  stage  are  very  compli- 
cated, depending,  as  they  do,  on  the  time  of  exposure  and  the 
temperature,  and  in  some  respects  resemble  a  reversible  reac- 
tion. The  aliphatic  hydrocarbons  are  on  one  hand  loosening 
their  carbon  bonds  and  splitting  off  the  initial  members  of 
their  series,  while  the  residues  unite  into  more  complex  carbo- 
cyclic  compounds.  Thus  benzol  compounds  under  the  heat 
influence  in  time  are  decomposed  with  the  liberation  of  hydro- 
gen, carbon  and  the  formation  of  still  higher  ring  compounds. 
On  the  other  hand,  the  free  hydrogen  present  reacts  on  the 
aliphatic  compounds. 

"It  is  this  stage  of  the  carbonization  that  is  radically  affected 
by  the  method  of  carbonization  that  is  employed." 

For  a  comprehensive  consideration  of  the  theories  of  the 
formation  of  the  individual  constituents  of  coal  tar,  reference 
should  be  made  to  the  investigations  of  Berthelot,  Jacobsen, 
Schulz,  Kohler,  Lewes,  Mills,  Bone  and  Coward  and  others 
who  have  made  a  study  of  this  subject.  While  none  of  the 
theories  which  have  been  advanced  is  satisfactory  in  every 
respect,  many  of  them  are  probably  correct  to  a  limited  extent. 
The  more  complex  hydrocarbons  can  be  theoretically  formed 
in  a  variety  of  ways  and  it  would  seem  likely  that  they  are 
thus  formed  under  the  varying  conditions  of  temperature, 
pressure  and  time  encountered  during  the  process  of  carbon- 
ization. If  during  the  first  and  second  stages  hydrocarbons 
containing  less  than  three  carbon  atoms  are  formed,  four  possi- 
ble compounds  might  be  produced,  CH4,  C2H6,  C2H4,  and 
C2H2.  Berthelot*  considers  that  these  compounds  may  com- 
bine and  polymerize  to  form  other  compounds  as  follows: 

*  "  Compt.  Rend.,"  Ixii,  pp.  905-947. 


TAR  AND  TAR  PRODUCTS  245 

2  CH4  =  C2H6  +  H2 
or     2  CH4  -  C2H2  +  3  H2 

C2HG  =  C,H4  +  H2 
2  C2H6  =  C,H2+  2  CH4  +  2H2 
C2H4  =  C2H2~  +  H2 

2  C,H4  =  C2H2  +  C2H6 

3  C2H2  =  C6H6  benzene 

4  C2H2  =  C8H8  styrolene 

C6H6  +  2  C2H2  =  C10H8  (napthalene)  +  H2 
2  C6H6  +  C2H2  =  C14H12(anthracene)  +  H2 

While  these  reactions  are  purely  speculative  and  open  to 
serious  criticism,  they  serve  the  purpose  of  showing  the  possi- 
ble methods  of  formation  of  coal  tar  constituents.  It  is  en- 
tirely probable  that  at  high  temperatures  the  hydrocarbons 
dissociate  into  radicals  or  residues  such  as  CH=,  CH2  = ,  CH3  — , 
which  under  the  varying  conditions  encountered  in  the  dis- 
tillation recombine  in  various  ways  to  form  other  coal  tar 
hydrocarbons,  or  else  split  up  into  the  elements  carbon  and 
hydrogen.  Such  a  theory  has  been  advanced  by  Bone*  and 
Coward  and  would  at  present  seem  to  be  the  most  generally 
acceptable.  Upon  such  an  assumption  if  nascent  C  =  and  H  - 
are  included,  the  formation  of  the  benzene  homologues  is  con- 
ceivable either  by  direct  union  of  these  residues  or  according  to 
the  theory  of  Jacobsen,  who 'assumes  allyene  (C3H4),  the  homo- 
logue  of  acetylene,  to  participate  in  the  reactions.  Thus  the 
formation  of  C3H4  is  made  possible  by  the  union  of  a  C  =  with 
a  CH=  and  a  CH3—  residue,  after  which  more  complicated 
residue  reactions  might  take  place  which  could  be  expressed  in 
condensed  form  according  to  Jacobsens'  f  reactions  as  follows : 

2  C2H2  +  C3H4  =  C7H8  toluene 
C2H2  +  2  C3H4  =  C,H10  xylenes 

3  C3H4  =  C9H12  mesitylene  and  pseudo-cumene. 

*  London  Journal,  Aug.  4,  1908,  p.  319. 
t  Ber.  Deutsch.  Chem.  Ges.,  1877,  p.  853. 


246  DUST   PREVENTIVES    AND    ROAD   BINDERS 

Whatever  the  exact  nature  of  these  reactions  may  be,  it  is 
certain  that  at  very  high  temperatures  an  ultimate  decompo- 
sition of  the  hydrocarbons  takes  place  with  the  formation  of  free 
carbon  and  free  hydrogen.  Any  scrubbing  action  to  which  the 
highly  heated  vapors  are  subjected  assists  in  this  decomposition, 
and  while  the  resulting  hydrogen  is  found  in  the  gas,  a  large  pro- 
portion of  th.e  carbon  is  deposited  in  the  tar.  This  decomposi- 
tion undoubtedly  occurs  to  the  greatest  extent  when  the  vapors 
come  in  contact  with  the  sides  of  the  retort  where  the  maxi- 
mum temperatures  prevail.  The  maximum  temperatures  may, 
therefore,  be  considered  as  responsible  for  the  formation  of  free 
carbon  in  tars.  This  may  be  quite  independent  of  the  average 
temperature,  as  will  be  shown  under  the  manufacture  of  water 
gas  tar,  where  higher  average  temperatures  are  encountered  but 
much  lower  maximum  temperatures.  It  is  because  of  lower 
temperatures  that  many  coke  oven  tars  contain  less  carbon 
than  gas  house  coal  tars. 

Water  Gas  Tar.  —  The  principle  of  making  water  gas  is  based 
upon  the  decomposition  of  steam  by  incandescent  carbonaceous 
materials.  Several  reactions  are  involved  according  to  tempera- 
ture and  pressure,  with  the  ultimate  formation  of  hydrogen  and 
carbon  monoxide.  These  reactions  for  the  sake  of  convenience 
may  be  condensed  to  the  following: 

C  +  H20  =  CO  +  H2. 

Ordinary  water  gas  may,  therefore,  be  considered  as  a  simple 
mixture  of  these  two  constituents.  As  no  hydrocarbons  are 
formed  in  this  process,  there  can  be  no  formation  of  tar.  Both 
hydrogen  and  carbon  monoxide,  however,  burn  with  a  non- 
luminous  flame,  which  makes  it  necessary  to  enrich  the  water 
gas  with  hydrocarbons  when  it  is  desired  to  produce  an  illu- 
minating gas.  A  petroleum  product  known  as  gas  oil  is  com- 
monly employed  for  this  purpose  and  the  resulting  gas  is  said 
to  be  enriched  or  carburetted.  In  the  carburetting  process  it 
becomes  necessary  to  heat  the  oil  in  a  peculiar  way  in  order 
to  produce  permanent  hydrocarbon  gases.  Other  hydrocarbons 


TAR   AND   TAR   PRODUCTS 


247 


are  formed  at  the  same  time,  which  pass  over  in  a  gaseous  state, 
but  later  condense  upon  cooling  to  form  the  water  gas  tar. 
It  will  be  seen  that  while  such  a  tar  is  produced  in  the  manu- 
facture of  carburetted  water  gas  it  is  in  reality  an  oil  tar. 
Several  methods  of  producing  carburetted  water  gas  have  been 
suggested  and  used,  but  one  known  as  the  intermittent  system 
has  been  most  generally  adopted.  Following  is  given  a  brief 
description  of  this  process,  which  is  illustrated  in  Fig.  22. 


FIG.  22.     Improved  Low  Carburetted  Water-gas  Plant. 

Coke  or  anthracite  coal  is  first  heated  to  redness  in  a  chamber 
A,  called  the  generator.  Air  is  then  admitted  to  the  generator 
through  the  blast  pipe  b,  which  passing  through  the  incandes- 
cent fuel  reacts  with  it  to  form  producer  gas.  The  hot  producer 
gas  passes  out  of  the  generator  into  the  top  of  the  chamber  C, 
called  the  carburettor,  where  it  meets  a  blast  of  air  from  pipe 
&',  and  is  partially  oxidized.  The  heat  of  combustion  raises  the 
temperature  of  the  checkerwork  of  brick  in  C.  The  uncon- 
sumed  gas  and  products  of  combustion  next  pass  into  the  cham- 
ber S,  known  as  the  superheater.  This  chamber  is  also  filled 
with  a  checkerwork  of  brick  which  becomes  heated  by  contact 
with  the  gases,  here  entirely  oxidized  by  air  admitted  through 


248  DUST   PREVENTIVES   AND    ROAD    BINDERS 

the  blast  pipe  b".  The  products  of  combustion  then  escape 
through  the  stack  valve  V  and  pass  up  the  stack  D.  This 
process  is  only  preliminary  to  the  actual  manufacture  of  water 
gas  and  is  continued  just  long  enough  to  bring  the  fuel  in  the 
generator  to  a  bright  red  heat  and  the  brick  checker  work 
in  the  carburettor  and  superheater  to  proper  temperature. 
When  this  is  accomplished  steam  is  admitted  into  the  generator 
through  the  pipe  s,  all  of  the  air  blasts  are  shut  off  and  the 
stack  valve  closed.  Water  gas  is  formed  in  the  generator  and 
passes  into  the  carburettor,  where  it  meets  a  spray  of  oil 
introduced  through  the  pipe  /.  The  oil  is  gradually  gasified  and 
carried  by  the  water  gas  into  the  superheater,  where  it  is 
broken  up  into  permanent  hydrocarbon  gases  by  the  high 
temperature,  and  also  tarry  products  which  condense  during 
the  process  of  gas  purification.  The  enriched  water  gas  passes 
from  the  superheater  through  the  pipe  g  to  a  series  of  washers 
and  scrubbers  quite  similar  to  those  described  under  the  manu- 
facture of  coal  tar.  Here  the  tarry  products  are  deposited  and 
afterwards  run  into  storage  tanks.  The  carburetting  process 
is  continued  as  long  as  the  fuel  in  the  generator  is  sufficiently 
high  to  produce  good  water  gas.  When  it  falls  below  this  point 
the  steam  and  oil  are  turned  off,  the  stack  valve  opened,  and  the 
blast  turned  on  in  order  to  again  heat  up  the  system.  When 
this  is  accomplished,  the  carburetting  process  is  repeated,  and 
so  on. 

Various  oils  are  employed  in  the  carburetting  process,  some 
being  crude  petroleum  and  some  especially  prepared  petroleum 
products,  known  as  gas  oils.  These  gas  oils  are  usually  dis- 
tillates falling  between  the  illuminating  oils  and  the  lubricating 
oils.  They  vary  greatly  in  character  and  therefore  cause 
considerable  variation  in  the  tars  which  they  produce  upon 
being  cracked.  As  in  the  formation  of  coal  tar  the  characteris- 
tics of  water  gas  tar  are  largely  dependent  upon  the  temperature 
at  which  it  is  produced.  As  a  rule  the  maximum  temperature 
is  not  sufficiently  high  to  form  any  considerable  amount  of  free 
carbon,  but  hydrocarbons  are  formed  in  much  the  same  manner 


TAR  AND   TAR   PRODUCTS  249 

as  in  the  formation  of  coal  tar  and  in  many  cases  are  identical 
with  the  coal  tar  hydrocarbons.  The  relative  proportions  of 
the  various  constituents  are,  however,  quite  different  from  the 
latter. 

Crude  water  gas  tar  is  a  thin  oily  liquid  having  a  specific 
gravity  lying  usually  between  i  and  i.i.  It  contains  large 
quantities  of  water,  from  which  it  is  often  partially  separated 
by  mechanical  devices  not  unlike  a  cream  separator.  This  par- 
tially dehydrated  tar  is  the  crude  water  gas  tar  of  commerce.  It 
has  a  strong  gassy  odor,  which,  if  it  is  used  as  a  dust  preventive, 
disappears  shortly  after  application.  Much  of  it  is  consumed 
as  fuel  by  gas  plants,  being  burnt  under  the  boilers  and  retorts. 
Quite  recently  attempts  have  been  made  to  refine  it  in  much 
the  same  way  that  coal  tars  are  refined.  Valuable  products 
have  thus  been  obtained,  both  as  distillates  and  residues.  The 
properties  of  an  average  sample  of  crude  water  gas  tar,  from  the 
standpoint  of  road  treatment,  are  shown  below. 

CRUDE    WATER    GAS    TAR. 

Character Thin,  oily 

Specific  gravity,  25°/25°  C i  .041 

Distillation: 

Water 2.4 

First  light  oils  to  110°  C.,  per  cent  by  vol 3.5 

Second  light  oils  no°-i7o°  C.,  per  cent  by  vol 18.  i 

Heavy  oils,  i7o°-27o°  C.,  per  cent  by  vol 52.0 

Pitch  residue  (by  difference)  per  cent  by  vol 24.0 


too.  o 


Pitch  residue  (per  cent  by  weight) 26.2 

Free  carbon i .  60% 

Remarks.  —  The  second  light  oils  showed  only  a  verv  small  amount  of  precipi- 
tate naphthalene  when  cold,  and  the  heavy  oils  none  at  all.  The  pitch  residue 
showed  a  very  lustrous  fracture. 

As  compared  with  crude  coal  tars  it  will  be  seen  from  the 
above  results  that  crude  water  gas  tar  is  a  very  much  lighter 
product,  the  specific  gravity  being  below  the  lowest  limit  of 
coal  tar.  The  water  which  it  contains  is  practically  free  from 
ammonia,  and  this  is  characteristic  of  the  material.  It  will  be 
noticed  that  all  of  the  distillates  are  comparatively  free  from 


250  DUST  PREVENTIVES   AND   ROAD   BINDERS 

naphthalene,  and  this  in  connection  with  the  low  free  carbon 
contents  makes  it  a  very  satisfactory  material  to  refine,  in  so  far 
as  the  production  of  a  road  binder  is  concerned.  The  high 
percentage  of  heavy  oils  and  low  percentage  of  pitch  residue 
make  it  an  exceedingly  poor  binder  in  its  natural  condition. 
It  has,  however,  valuable  properties  as  a  dust  preventive  and 
can  be  satisfactorily  applied  by  means  of  an  ordinary  watering 
cart.  It  compares  very  favorably  with  some  of  the  lighter 
petroleum  products  and  emulsions  when  used  for  this  purpose. 
Its  odor  is  rather  disagreeable  at  first,  but  disappears  shortly 
after  application  has  been  made  to  a  road  surface.  When  mixed 
in  suitable  proportions  with  crude  coal  tar  it  forms  a  good  tern- 
porary  binder,  which  may  be  applied  cold.  Its  greatest  value 
for  road  purposes,  however,  is  its  ability  to  produce  a  very 
excellent  soft  tar  pitch  when  properly  refined. 

In  many  gas  plants  it  is  the  custom  to  manufacture  both 
coal  gas  and  carburetted  water  gas.  When  this  is  done  the 
coal  gas  is  produced  at  a  high  temperature  in  order  to  obtain 
the  maximum  yield,  and  the  carburetted  water  gas  is  used  to 
raise  its  illuminating  value.  In  such  plants  the  coal  tar  is 
unsuited  for  road  work.  Sometimes  both  the  water  gas  tar 
and  coal  tar  are  run  together  into  the  same  well,  thus  produc- 
ing a  mixture  of  the  two.  This  mixture  will  be  of  an  inferior 
quality  for  road  treatment  for  reasons  which  have  been  pre- 
viously discussed.  It  may,  however,  sometimes  be  distilled  to 
produce  a  fairly  good  road  binder.  This  is  largely  dependent 
upon  the  amount  of  water  gas  tar  present,  which  serves  to  cut 
down  the  percentage  of  free  carbon  in  the  refined  product. 

Oil  Gas  Tar.  —  Tars  formed  in  the  manufacture  of  straight 
oil  gas  require  but  passing  mention,  as  they  are  not  produced 
in  very  large  quantities  and  have  not  to  the  author's  knowledge 
been  used  to  any  extent  in  the  treatment  of  roads.  There  are 
a  number  of  processes  for  producing  oil  gas,  the  most  common 
being  the  Pintsch  system  and  the  Peebles  process.  They  are 
all  dependent  upon  the  cracking  of  oil  vapors  in  especially  con- 
structed retorts,  with  the  formation  of  permanent  gases  and 


TAR   AND   TAR   PRODUCTS  251 

tarry  condensations  of  varied  character.  In  some  of  these 
processes  the  tar  itself  is  again  cracked,  so  that  in  the  end  little 
but  hydrocarbon  gases  and  free  carbon  are  produced. 

The  Effect  of  Free  Carbon  in  Tars.  —  The  effect  of  free 
carbon  in  tars  from  the  standpoint  of  road  treatment  has  been 
studied  by  the  author  and  the  results  of  his  investigations  pre- 
sented in  a  recent  paper,*  which  is  quoted  below  at  some 
length. 

If  a  drop  of  tar  is  examined  under  the  microscope  it  will  be 
seen  to  consist  of  a  more  or  less  homogeneous  liquid,  which  by 
transmittant  light  gives  a  reddish  brown  color,  and  in  which 
float  small  black  amorphous  particles.  It  will  also  be  noticed 
that  the  number  of  these  particles  varies  enormously  with 
different  samples  of  tar.  Under  high  magnification  some  of 
these  particles  or  clumps  of  particles  resemble  irregular  shaped 
lumps  of  coal,  while  others  are  so  small  as  to  be  almost  sub- 
microscopic.  If  a  small  quantity  of  tar  is  diluted  with  a  proper 
solvent,  such  as  benzol  or  carbon  bisulphide,  the  solution  passed 
through  a  filter  and  the  residue  which  is  retained  upon  the 
filter  thoroughly  washed  with  the  solvent,  a  black  amorphous 
powder  will  be  obtained,  which,  when  examined  under  the 
microscope,  can  be  identified  as  the  floating  particles  which 
were  found  to  exist  in  the  original  tar.  This  material  is  com- 
monly known  as  free  carbon. 

The  presence  of  free  carbon  in  any  considerable  quantity 
may  affect  the  physical  properties  of  tars  in  two  ways:  (i) 
either  mechanically  by  its  actual  presence  or  (2)  by  the  pres- 
ence of  other  substances  which  were  formed  with  it  at  high 
temperatures.  To  test  its  mechanical  effect  a  gas  house  tar 
was  selected  which  was  found  to  contain  29.2  per  cent  free 
carbon.  A  quantity  of  this  tar  after  dehydration  was  diluted 
with  coal  tar  benzol  and  quickly  filtered  through  a  folded  filter 
paper  in  order  to  remove  most  of  the  free  carbon.  The  filtrate 
was  then  evaporated  on  a  steam  bath  beside  a  fresh  sample  of 

*  "  The  Effect  of  Free  Carbon  in  Tars  from  the  Standpoint  of  Road  Treatment." 
Proceedings  of  the  American  Society  for  Testing  Materials,  Vol.  IX,  1909,  p.  549. 


252 


DUST   PREVENTIVES   AND    ROAD   BINDERS 


the  dehydrated  tar  until  no  odor  of  benzol  could  be  detected  in 
either  sample,  and  the  evaporation  continued  until  both  samples 
showed  the  same  rate  of  flow  and  approximately  the  same  con- 
sistency as  determined  by  the  float  test. 

Determinations  made  upon  the  filtered  and  unfiltered  tars, 
prepared  in  the  manner  described,  showed  them  to  contain 
4.4  per  cent  and  31.0  per  cent  free  carbon  respectively.  By 
mixing  proper  proportions  of  these  tars  two  other  samples  were 
obtained,  one  of  which  held  10  per  cent  and  the  other  20  per 
cent  free  carbon.  The  samples  were  then  given  numbers  from 
i  to  4  as  the  free  carbon  contents  increased.  The  relative 
cohesive  or  binding  strength  of  these  samples  was  next  deter- 
mined by  means  of  a  machine  especially  designed  for  this  pur- 
pose. The  results  as  given  in  Table  I  show  the  maximum 
resistance  in  pounds,  which  was  offered  to  a  breaking  load 
applied  in  tension  to  a  layer  of  the  tar  held  between  two  metal 
surfaces,  the  reading  being  obtained  by  means  of  a  spring 
balance  to  which  one  of  the  metal  contacts  was  attached.  The 
thickness  of  the  layer  of  tar  was  identical  in  every  test,  as  well 
as  all  other  conditions,  such  as  temperature,  etc.,  so  that  the 
results  obtained  are  strictly  comparable. 

TABLE    I. 


Sample  No    

i 

2 

3 

Free  carbon  

4-4% 

10.0% 

20.0% 

31-0% 

Binding  strength  at  25°  C.,  Test  i.  .  .  . 
Binding  strength  at  25°  C.,  Test  2.  ... 

18  Ib. 
19  Ib. 

7.5  Ib. 

8      Ib. 

4lb. 
4lb. 

3lb. 
3lb. 

From  this  table  it  will  be  seen  that  the  cohesive  or  binding 
strength  is  almost  inversely  proportional  to  the  amount  of  free 
carbon  present.  It  should  be  remembered,  however,  that  these 
tars  are  of  approximately  the  same  consistency  and  obtained 
from  the  same  source,  and  that  this  relation  would  not  neces- 
sarily or  even  probably  hold  good  for  different  tars  of  different 
consistencies. 


TAR   AND   TAR   PRODUCTS 


253 


While  the  binding  strength  of  a  tar  is  one  of  its  most  impor- 
tant properties  from  the  standpoint  of  road  treatment,  there 
are  others  fully  as  important.  Its  waterproofing  quality  when 
employed  in  a  mineral  aggregate  should  be  considered,  and  for 
this  purpose  a  number  of  sand-tar  briquettes  were  made  up 
with  equal  quantities  of  tar  and  their  absorption  in  water 
determined. 

The  sand  used  in  this  and  all  of  the  other  sand-tar  experi- 
ments was  a  common  river  sand  which  had  been  thoroughly 
dried  and  passed  through  a  10  mesh  sieve.  It  was  found  to  con- 
tain 37  per  cent  voids  when  consolidated,  and  when  mechani- 
cally separated  showed  the  following  percentage  of  various  sized 
grains.  Its  specific  gravity  was  2.68. 


Sand. 

Per    cent. 

Pas 

sing  200  m< 

100 

80 

50 

40 

3° 
20 

;sh  sie 

ve 

6 

2 
2 

18 
8 

38 

26 

100 

The  sand-tar  mixtures  were  carefully  prepared  in  metal  cups 
heated  by  means  of  a  low  flame  in  such  a  manner  that  at  all 
times  the  handle  of  the  cup  could  be  held  without  burning  the 
flesh.  But  very  little  loss  by  volatilization,  therefore,  occurred. 

In  the  following  experiments  6  parts  by  weight  of  tar  were 
stirred  with  100  parts  by  weight  of  sand,  until  the  mixture  was 
to  all  appearances  absolutely  uniform.  While  still  warm  the 
mixtures  were  pressed  by  hand  into  ordinary  cement  molds  and 
allowed  to  cool.  They  were  then  removed  from  the  mold, 
weighed  and  placed  under  water  for  24  hours,  after  which  they 
were  drained  free  from  surplus  water,  wiped  with  a  soft  towel 
and  again  weighed.  The  gain  in  weight  was  calculated  upon 
a  percentage  basis  as  water  absorbed,  and  the  results  so  obtained 
are  given  in  Table  II.  , 


254  DUST   PREVENTIVES   AND    ROAD    BINDERS 

TABLE    II. 


Sample  No    . 

i 

2 

Per  cent  free  carbon  in  binder 

4  4 

IO    O 

20  o 

•31      O 

Weight  briquette  dry  (gms.)  
Water  absorbed  

111.52 

7.r0% 

no.  64 

4.15% 

109.35 

6.10% 

lOQ.  12 
IO.OQ% 

• 

It  will  of  course  be  noticed  that  the  percentage  of  water  ab- 
sorbed increases  with  the  percentage  of  free  carbon  present  in 
the  binder.  The  same  modifying  factors  mentioned  under  the 
binding  strength  tests,  however,  should  be  considered  in  con- 
nection with  the  above  results. 

While  all  of  the  tar  samples  in  the  preceding  tests  were  of 
about  the  same  consistency,  it  was  realized  that  the  actual 
bitumen  contained  could  not  be  of  the  same  consistency  in  the 
different  samples,  for  the  reason  that  if  a  quantity  of  any  inert 
power  is  added  to  a  tar  the  consistency  of  the  mixture  will  be 
greater  than  that  of  the  original  tar.  In  order  to  obtain  some 
idea  as  to  the  mechanical  effect  of  free  carbon  upon  tar  bitu- 
mens of  a  given  consistency,  a  dehydrated  coke  oven  tar, 
called  sample  5,  containing  7.0  per  cent  free  carbon,  was  selected 
and  to  a  portion  of  this  tar  lampblack  was  added  in  quantity 
sufficient  to  raise  the  free  carbon  contents  to  25  per  cent. 
This  mixture  was  called  sample  6.  The  use  of  lampblack  as 
a  substitute  for  free  carbon  is  certainly  subject  to  criticism,  but 
it  was  selected  by  the  writer  as  more  nearly  resembling  free 
carbon  than  anything  else  that  could  readily  be  obtained. 
The  addition  of  this  substance  increased  the  consistency  of  the 
tar  considerably,  and  determinations  of  the  relative  binding 
strength  of  the  two  samples  made  in  the  manner  previously 
described  showed  a  considerable  gain  in  strength  for  the  tar  to 
which  it  had  been  added.  The  results  so  obtained  are  given  in 
Table  III.  These  tests  would  seem  to  show  that  the  presence 
of  free  carbon  in  tar  bitumens  of  a  given  consistency  increases 
the  cohesive  or  binding  strength  of  the  niaterial. 


TAR  AND  TAR  PRODUCTS 
TABLE  III. 


255 


Sample  No                                  

5 

6 

Free  carbon                                     

7.0% 

2C.O% 

Binding  strength  at  25°  C  ,  Test  i  

13.5  lb. 

20+    lb. 

Binding  strength  at  25°  C     Test  2 

1U 

13  Ibs 

20+  Ibs 

NOTE.  —  Twenty  pounds  was  the  limit  of  the  machine. 

Sand  briquettes  were  next  made  with  these  samples,  as  in 
the  other  tests,  using  6  parts  by  weight  of  tar  to  100  parts  by 
weight  of  sand.  While  the  briquette  made  with  No.  5  could 
be  handled  without  breaking,  that  made  with  No.  6  would  not 
hold  together,  showing  that,  notwithstanding  the  fact  that  the 
binding  strength  of  the  tar  had  been  increased  by  the  addition 
of  carbon,  its  binding  capacity  had  been  diminished.  In  order 
to  compare  the  relative  waterproofing  qualities  of  these  two 
materials,  it  was  found  necessary  to  make  a  briquette  with 
No.  6  which  should  have  a  bitumen  equivalent  of  No.  5,  and 
this  was  accomplished  by  using  7.44  parts  of  No.  6  in  place  of 
6  parts.  From  the  results  of  these  absorption  tests  made  in 
exactly  the  same  manner  as  described  in  the  other  experi- 
ments it  will  be  seen  that  here  again  the  percentage  of  water 
absorbed  increases  with  the  percentage  of  free  carbon  con- 
tained in  the  binder.  These  results  are  given  in  Table  IV. 

TABLE    IV. 


Sample  No  

5 

6 

Free  carbon          .    . 

y.0% 

2 

2cr  o% 

Amount  of  binder  in  briquette  

6.00% 

6.00% 

7    44% 

\Vater  absorbed 

I    04% 

Crumbled 

•?    77% 

When  applying  tar  to  an  old  road  surface,  to  insure  lasting 
results  it  is  most  important  that  the  tar  should  penetrate  the  sur- 
face of  the  road  to  a  considerable  extent.  To  determine  the 
effect  which  free  carbon  would  have  upon  this  property  three  coal 


256 


DUST   PREVENTIVES   AND    ROAD   BINDERS 


tars  containing  different  amounts  of  free  carbon  were  selected. 
These  tars  were  numbered  7,  8,  and  9,  in  the  order  of  their 
free  carbon  contents,  and  were  painted  upon  unglazed  porcelain 
tiles,  the  thickness  of  each  coat  being  made  as  nearly  the  same 
as  possible.  After  the  painted  surfaces  had  dried  off,  the  tiles 
were  broken  and  the  average  penetration  measured.  The 
results  so  obtained  are  given  in  Table  V,  and  indicate  that 
free  carbon  seriously  affects  the  penetrating  value  of  tars. 

TABLE    V. 


Sample  No  

7 

8 

Free  carbon  

6.7% 

2Q    2% 

1O    0% 

One  coat  of  tar  penetration  

A* 

9  2  » 

2" 

Three  coats  of  tar  penetration 

S" 

Kl 
A* 

A" 

ffj 

Wi 

61 

The  surface  coat  of  bitumen  was  next  scraped  from  the  tiles 
with  a  knife.  No.  7  was  very  sticky  and  difficult  to  remove, 
Nos.  8  and  9  could,  however,  be  readily  peeled  off,  and  the  skin 
of  bitumen  thus  obtained  was  in  each  case  much  less  sticky 
than  No.  7  and  quite  short. 

With  the  exception  of  the  tile  tests  all  of  the  experiments  so 
far  described  have  had  to  do  with  the  mechanical  effect  of  free 
carbon  on  practically  the  same  kind  of  bitumen.  The  fact  that 
differences  in  character  of  the  bitumens  found  in  low  and  high 
carbon  tars  may  affect  the  physical  properties  of  the  tars  has 
already  been  mentioned,  and  in  order  to  study  the  effect  of  both 
together,  representative  samples  of  low,  medium  and  high 
carbon  tars  were  taken  for  the  following  experiments.  As  the 
consistency  of  the  tars  employed  in  the  preceding  experiments 
was  not  great  enough  to  produce  sand-tar  briquettes  which 
could  be  successfully  tested  for  strength,  it  was  thought  advis- 
able to  reduce  these  tars  to  the  consistency  of  medium  soft 
pitches,  such  as  might  be  employed  in  road  construction.  While 
the  penetration  test  is  usually  employed  to  determine  the  con- 
sistency of  such  materials,  the  melting  point  as  determined  by 


TAR    AND   TAR   PRODUCTS 


257 


the  well-known  cube  test  is  generally  used  in  grading  pitches, 
and  for  a  number  of  reasons  it  was  decided  to  make  use  of  this 
test  as  a  basis  of  comparison.  In  the  first  place,  if  all  of  the 
samples  were  found  to  have  the  same  penetration  at  a  given 
temperature  it  would  not  necessarily  follow  that  they  would 
have  the  same  relative  penetration  at  another  temperature. 
Moreover  it  was  feared  that  the  presence  of  free  carbon  would 
seriously  affect  the  movement  of  the  needle,  so  that  the  actual 
consistency  of  the  bitumen  present  would  not  be  indicated.  By 
experiment  this  was  found  to  be  true  at  ordinary  temperatures, 
although  at  low  temperatures  the  effect  of  the  carbon  appeared 
to  be  lessened.  On  the  other  hand,  the  melting  point  was 
believed  to  more  nearly  represent  the  actual  consistency  of  the 
bitumen  present.  For  the  sake  of  comparison,  however,  results 
of  both  the  penetration  and  float  tests  are  given  in  Table  VI. 

TABLE    VI. 


Sample  No. 

I  O 

1  1 

Kind  of  tar 

\Vater  gas 

Coke  oven 

Gas  H 

Free  carbon           ...        ... 

i  60% 

12    OO% 

3<    7O% 

Melting  point  

<o°C 

<?o°C 

v)D-  l~fv 
SO°C 

PENETRATION  TESTS. 
No.  2  needle,  5  sec.,  100  gms.,  25°  C  

44 

qo 

«r6 

No.  2  needle,  next  5  sec.,  100  gms.,  25°  C  
No.  2  needle,  next  5  sec.,  100  gms.,  25°  C  
No    2  needle,  i  min  ,  200  gms  ,  5°  C     .... 

16    . 

12 

6 

22 
17 

6 

24 

20 

6 

Float  test  at  60°  C  

194  sec 

185  sec 

•5-24.  sec 

The  tars  selected  were  a  Philadelphia  water  gas  tar  called 
sample  10,  a  Birmingham  coke  oven  tar  called  sample  n,  and 
a  Providence  gas  house  tar  called  sample  12.  Fairly  large 
portions  of  these  materials  were  evaporated  in  a  hot  air  oven 
until  their  melting  points  were  50°  C.,  the  temperature  of  the 
oven  at  no  time  being  allowed  to  exceed  250°  C.  Sand  tar 
mixtures  with  varying  proportions  of  binder,  as  shown  in  tables 
VII  and  VIII,  were  then  made  up,  and  these  mixtures  molded 
into  briquettes  in  the  following  manner. 


258  DUST   PREVENTIVES    AND    ROAD   BINDERS 

Twenty  grams  of  the  mixture  was  weighed  out  and  placed  in 
a  cylindrical  metal  mold  carrying  a  close  fitting  plunger.  Pres- 
sure was  then  applied  by  means  of  a  small  Olsen  Testing  Machine 
run  at  a  constant  speed.  All  of  the  mixtures  were  subjected 
to  a  pressure  of  1425  Ibs.  and  the  briquettes  thus  formed  measured 
25  mm.  in  diameter  and  approximately  25  mm.  in  height.  There 
was  no  particular  reason  for  making  the  briquettes  in  just  this 
manner,  except  that  the  method  conformed  to  the  general 
method  employed  by  the  Office  of  Public  Roads  in  making 
rock  dust  briquettes  for  the  cementation  test. 

As  soon  as  they  were  made  three  briquettes  of  each  mixture 
were  placed  in  a  refrigerator  for  30  minutes,  after  which  they 
were  immersed  in  ice  water  at  5°  C.  for  30  minutes  and  tested 
under  water  at  this  temperature  in  the  Olsen  Testing  Machine, 
which  was  run  at  a  definite  speed.  Tests  were  made  in  com- 
pression, and  the  maximum  resistance  offered  by  the  briquettes 
noted.  Check  tests  of  the  same  mixtures  varied  somewhat, 
as  shown  in  the  following  tables,  but  it  is  believed  that  a  com- 
parison of  the  average  results  will  prove  of  considerable  value 
in  determining  the  effect  of  free  carbon  upon  the  binding  values 
of  the  tars.  Slight  variations  in  the  method  of  making  the 
tests  were  found  to  cause  considerable  variations  in  results,  so 
that  it  was  necessary  to  take  every  precaution  to  duplicate  the 
exact  conditions  under  which  each  of  these  tests  were  made. 

The  following  tables  are  self-explanatory,  so  that  it  seems 
unnecessary  to  describe  them  further  than  to  say  that  two 
series,  one  with  6  per  cent  binder  and  the  other  with  10  per  cent 
binder,  were  made  in  such  a  manner  that  comparisons  upon 
both  a  percentage  binder  and  maximum  and  minimum  per- 
centage bitumen  bases  could  be  drawn.  In  these  briquette 
tests  the  percentage  of  all  constituents  is  based  upon  the  weight 
of  sand  taken  as  100. 

In  considering  the  compression  tests  in  Table  VII  it  will  be 
seen  that  for  equal  quantities  of  binder  the  low  carbon  tar  has  a 
greater  binding  strength  than  either  of  the  others,  and  that  the 
medium  carbon  tar  gives  higher  results  than  the  high  carbon 


TAR   AND    TAR   PRODUCTS 


259 


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DUST   PREVENTIVES   AND   ROAD   BINDERS 


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NOTE 
of  >)itumen 

TAR    AND   TAR   PRODUCTS  261 

tar.  For  equal  quantities  of  bitumen  on  the  basis  of  the  mini- 
mum amount  present,  as  shown  by  No.  12,  results  are  nearly 
the  same  for  all  of  the  tars.  Upon  a  maximum  bitumen  basis 
as  shown  by  No.  10,  the  results  are,  however,  reversed.  The 
explanation  for  this  lies  in  the  fact  that  when  considerable 
quantities  of  free  carbon  are  present  the  carbon  acts  as  a  filler 
and  adds  to  the  mechanical  strength  of  the  mineral  aggregate. 
This  is  shown  in  Table  VIII  under  the  heading  Minimum  Per 
Cent  Bitumen,  in  which  the  percentage  of  bitumen  is  almost 
the  same  as  in  the  last  tests  mentioned  in  Table  VII.  It  will, 
however,  be  noticed  that  where  an  amount  of  limestone  dust  is 
added  in  sufficient  quantity  to  produce  an  equivalent  weight 
of  filler  that  the  strength  developed  by  the  same  per  cent  of 
bitumen  is  again  almost  the  same  for  the  different  tars.  This 
is  an  important  consideration  from  the  standpoint  of  road 
construction. 

In  Table  VIII,  where  an  equivalent  amount  of  binder  is 
employed,  it  will  be  seen  that  the  same  general  relations  hold 
good  as  shown  under  similar  conditions  in  Table  VII.  The 
differences  are,  however,  not  so  marked  because  of  the  more 
prominent  part  played  by  free  carbon  as  a  filler.  It  should  be 
remembered,  however,  that  in  ordinary  bituminous  macadam 
construction  over  6  per  cent  bitumen  is  seldom  employed  in  the 
mineral  aggregate,  and  that  as  this  aggregate  is  much  coarser 
than  the  sand  used  in  the  tests,  the  action  of  the  relatively 
small  amount  of  carbon  as  a  filler  is  hardly  worth  considering. 
The  results  given  in  Table  VIII  under  the  heading  Maximum 
Per  Cent  Bitumen,  tend  to  show  much  the  same  thing  as  the 
Minimum  Per  Cent  Bitumen  Tests,  although  here  the  high 
carbon  tar  shows  up  to  even  less  advantage.  Considered  as 
a  whole  these  tests  show  the  mechanical  effect  of  free  carbon, 
but  would  not  seem  to  indicate  that  the  bitumen  present  in 
low  and  high  carbon  tars  varies  greatly  in  binding  value. 

Absorption  tests  made  upon  these  briquettes  show  in  both 
Tables  VII  and  VIII  that  where  equivalent  quantities  of 
binder  are  employed  those  briquettes  which  are  made  with  the 


262  DUST   PREVENTIVES    AND    ROAD    BINDERS 

high  carbon  tar  are  somewhat  less  waterproof  than  the  lower 
carbon  tars.  In  Table  VII  the  same  general  relations  seem  to 
hold  good  for  the  maximum  and  minimum  bitumen  tests,  but  in 
Table  VIII  in  the  bitumen  equivalent  tests  the  excess  of  bitumen 
coated  carbon  seems  to  have  lowered  the  absorptive  capacity 
of  the  briquettes.  A  still  further  lowering  is,  however,  ob- 
served where  limestone  dust  has  been  added  in  the  briquettes 
made  with  low  carbon  tars,  and  the  superiority  as  a  filler  of 
limestone  over  carbon  again  indicated.  In  considering  these 
tests  as  a  whole  it  might  be  remarked  that  a  slight  superiority 
in  waterproofing  power,  of  the  bitumens  contained  in  No.  n 
over  the  other  tars  is  indicated,  although  this  difference  is  by 
no  means  great. 

One  other  important  property  of  tars  from  the  standpoint  of 
road  treatment  which  has  not  yet  been  considered  is  the  relative 
amount  of  volatilization  which  may  be  expected  to  take  place 
on  a  tar  treated  road.  Some  of  the  constituents  of  all  tars  will 
volatilize  at  ordinary  temperatures,  thus  making  the  residue 
more  and  more  brittle  and  lessening  its  life.  It  is  believed  by 
some  that  the  presence  of  free  carbon  retards  this  volatilization, 
and  the  reason  for  this  belief  lies  in  the  fact  that  in  both  evapora- 
tion and  distillation  tests  a  film  of  carbon  forms  upon  the  surface 
of  the  hot  tar  and  retards  to  a  considerable  extent  the  volatiliza- 
tion of  the  lighter  constituents.  In  evaporating  the  three  tars 
which  were  employed  in  all  of  the  later  tests,  this  effect  was 
made  very  evident  by  the  time  required  to  bring  No.  12  to  the 
proper  consistency  as  compared  with  that  necessary  to  bring 
the  other  samples  to  the  same  consistency.  When  tar  is  em- 
ployed in  road  work,  however,  conditions  are  somewhat  different, 
for  here  the  tar  does  not  exist  in  thick  layers,  but  is  distributed 
over  the  surface  of  the  particles  composing  the  mineral  aggre- 
gate in  comparatively  thin  films.  In  order  to  determine  whether 
or  not  free  carbon  retards  volatilization  under  these  conditions, 
it  was  thought  well  to  subject  some  of  the  sand-tar  briquettes 
to  a  volatilization  test.  Briquettes  composed  of  different  mix- 
tures were  therefore  carefully  weighed  upon  watch  glasses  and 


TAR  AND  TAR  PRODUCTS  263 

placed  in  a  hot  air  oven  maintained  at  a  uniform  temperature 
of  1 00°  C.  for  four  consecutive  periods  of  five  hours  each.  The 
loss  in  weight  for  each  period  was  determined  and  the  per- 
centage loss  upon  the  basis  of  bitumen  present,  calculated.  The 
results  so  obtained  are  given  in  Table  VIII.  The  first  fact  to 
be  noted  is  that  the  greatest  loss  in  every  case  occurred  during 
the  first  period,  and  that  the  greatest  differences  between  in- 
dividual tests  are  here  made  apparent.  During  the  next  three 
periods  the  loss  by  volatilization  seems  to  be  practically  con- 
stant and  quite  uniform  for  the  different  briquettes.  In  the 
first  period  it  will  be  noticed  that  the  higher  the  percentage  of 
free  carbon  the  greater  the  loss  by  volatilization,  and  if  these 
results  alone  were  considered  one  might  naturally  come  to  the 
conclusion  that  the  presence  of  free  carbon  increased  the  vola- 
tility of  the  tar.  In  view  of  the  general  uniformity  of  the  next 
three  tests  this  opinion  would  have  to  be  modified,  and  the  only 
reasonable  conclusion  would  seem  to  be  that  under  the  given 
conditions  free  carbon  is  mechanically  inert  so  far  as  volatiliza- 
tion is  concerned.  It  would  seem,  however,  that  in  tars  of  the 
same  melting  point  the  percentage  of  highly  volatile  constitu- 
ents increases  as  the  percentage  of  free  carbon  increases,  and 
that  a  greater  loss  by  volatilization  would  occur  in  high  carbon 
tars  than  in  low  carbon  tars  under  conditions  encountered  in 
tar  treated  roads.  That  the  thickness  of  the  tar  film  has  con- 
siderable effect  upon  the  volatility  of  the  tar  is  indicated  by  the 
fact  that  in  nearly  every  case  less  loss  by  volatilization  occurred 
in  the  maximum  bitumen  tests  than  in  the  corresponding  mini- 
mum bitumen  tests.  In  this  connection  it  might  be  said  that 
one  of  the  advantages  of  employing  a  flush  coat  of  tar  in  bitu- 
minous road  construction  is  made  apparent,  as  a  coat  so  applied 
retards  the  volatilization  of  the  thinner  underlying  films  of  tar, 
and  therefore  prolongs  the  life  of  the  road. 

Before  summarizing  the  results  of  the  experiments  presented 
in  this  paper  it  may  be  well  to  mention  one  other  property  of 
tars  and  its  possible  relation  to  the  free  carbon  contents',  i.e., 
the  relative  susceptibility  to  temperature  changes  shown  by 


264  DUST   PREVENTIVES   AND    ROAD    BINDERS 

bitumens  contained  in  different  tars.  Owing  to  the  fact  that 
free  carbon  if  present  in  any  quantity  seriously  interferes  with 
a  correct  determination  of  the  consistency  of  the  accompanying 
bitumen,  it  would  seem  necessary  to  completely  remove  the 
carbon  before  attempting  to  determine  the  susceptibility  of 
the  bitumen  to  temperature  changes.  As  such  bodies  as  naph- 
thalene and  anthracene,  which  crystallize  at  comparatively 
high  temperatures,  usually  occur  in  greater  quantities  in  high 
carbon  than  in  low  carbon  tars,  it  would  seem  reasonable  to 
suppose  that  the  bitumen  obtained  from  the  former  would  be 
more  susceptible  to  temperature  changes.  This  is  an  important 
point  to  be  determined  and  one  which  the  writer  proposes  to 
follow  up.  As  it  is  only  indirectly  related  to  the  subject  of 
this  paper  it  will  not  be  further  discussed  at  this  time. 

Upon  reviewing  all  of  the  results  presented  it  is  believed  that 
the  following  facts  have  been  demonstrated  with  respect  to  the 
effect  of  free  carbon  in  tars: 

(1)  That  in  tars  of  the  same  consistency  those  of  low 
carbon  contents  have  a  greater  inherent  binding  strength 
than  those  of  high  carbon  contents. 

(2)  That  in   tars  whose  bitumen   contents   are  of  the 
same  consistency  those  of  high  carbon  contents  have  a 
greater  inherent  binding  strength  than  those  of  low  carbon 
contents,  but  that  the  binding  capacity  of  the  former  is 
lower. 

(3)  That  in  sand-tar  mixtures  containing  a  relatively 
large  amount  of  high  carbon  tar,  the  carbon  may  act  as  a 
filler  and  add  to  the  mechanical  strength  of  the  mineral 
aggregate,  but  that  better  results  in  this  respect  can  be 
obtained  by  the  use  of  a  smaller  quantity  of  low  carbon  tar 
of  the  same  melting  point,  together  with  a  mineral  filler. 

(4)  That  the  waterproofing  value  of  high  carbon  tars 
is  in  general  less  than  that  of  low  carbon  tars. 

(5)  That  free  carbon  retards  the  absorption  of  tars  by 
porous  surfaces. 


TAR   AND   TAR   PRODUCTS  265 

(6)    That  when  tar  is  exposed  in  comparatively  thin  films 
free  carbon  has  little  or  no  effect  in  retarding  volatilization. 

Applying  these  facts  to  the  use  of  tar  in  road  treatment  the 
following  conclusions  are  logically  deduced: 

(1)  In  the  treatment  of  old  road  surfaces  a  low  carbon 
tar  is  to  be  greatly  preferred  to  a  high  carbon  tar. 

(2)  In  ordinary  bituminous  road  construction,  both  from 
the  standpoint  of  efficiency  and  economy,  a  low  carbon 
tar  is  to  be  preferred  to  a  high  carbon  tar  whose  bitumen 
content  is  of  the  same  consistency. 

In  conclusion  it  might  be  said  that  to  the  writer's  knowledge 
no  reliable  comparative  data  as  to  the  actual  service  results 
obtained  by  the  use  of  high  and  low  carbon  tars  in  road  work 
is  at  present  available.  A  road  engineer  in  one  locality  may 
have  obtained  more  satisfactory  results  from  the  use  under  cer- 
tain conditions  of  a  high  carbon  tar  of  a  certain  consistency  than 
another  engineer  in  a  different  locality  using  a  low  carbon  tar 
of  different  consistency  under  different  conditions,  and  vice 
versa.  Many  other  factors  besides  the  free  carbon  contents 
have  to  be  considered  in  forming  a  correct  opinion  of  the  rela- 
tive value  of  two  tars.  The  writer  also  realizes  that  laboratory 
results  do  not  always  conform  to  actual  service  results,  but 
they  afe  nevertheless  often  of  considerable  value  to  those  who 
are  studying  a  subject  from  a  practical  standpoint.  It  might 
be  added  that  results  so  far  obtained  seem  to  substantiate  the 
general  conclusions  presented  in  this  paper. 

Tar  Refining.  —  With  the  development  of  the  coal  tar  indus- 
tries the  refining  of  crude  tars  has  become  necessary,  and  a 
great  deal  of  tar  now  produced  is  subjected  to  fractional  dis- 
tillation for  the  separation  of  certain  constituents  which  are 
used  in  the  arts.  The  method  of  distillation  varies  somewhat 
as  the  market  value  of  the  distillates  fluctuates.  Germany  is 
greatly  in  advance  of  this  country  at  the  present  time  in  refin- 
ing tar,  and  a  brief  consideration  of  the  general  method  employed 
in  that  country  should  be  of  value  in  obtaining  some  idea  of 


266 


DUST   PREVENTIVES   AND    ROAD    BINDERS 


its  various  constituents.  For  a  full  consideration  of  the  pro- 
cess of  tar  refining  reference  should  be  made  to  a  treatise  on 
the  subject  by  Lunge.* 

The  ordinary  refining  still  consists  of  a  vertical  wrought  iron 
cylinder  with  a  dome-shaped  top  and  concave  bottom,  as 
shown  in  Fig.  23.  The  top  is  provided  with  an  inlet  A  for  the 


FIG.  23.     German  Type  of  Tar  Still  and  Condenser. 

tar,  and  a  large  curved  outlet  pipe  B  for  the  vapors,  the  con- 
cave bottom  facilitating  the  distribution  of  heat  into  the  inte- 
rior of  the  charge  of  tar.  The  still  is  fire  heated  at  first,  but 
toward  the  end  of  the  process  superheated  steam  is  forced 
through  the  coil  C  to  aid  in  the  distillation  of  the  heavier  prod- 
ucts. A  draw-off  D  allows  the  residual  pitch  to  be  removed 
while  hot.  These  stills  have  a  capacity  of  from  ten  to  twenty 
tons.  The  outlet  pipe  leads  to  the  condenser  E,  which  is  an 
iron  or  lead  worm  placed  in  a  tank  of  water.  The  operation  of 
distillation  or  fractionation  consists  in  heating  the  charge  of 
tar  carefully  until  drops  of  liquid  come  from  the  still.  The  fire 
then  has  to  be  moderated  until  all  volatile  material  up  to 
105°  G.  is  removed  in  order  to  prevent  boiling  over.  As  the 
more  volatile  products  are  removed  the  temperature  rises,  and 

*  "  Coal  Tar  and  Ammonia."     Gurney  and  Jackson. 


TAR   AND   TAR   PRODUCTS  267 

the  point  where  distillation  is  stopped  depends  upon  the  prod- 
ucts which  it  is  desired  to  obtain.  Usually  five  fractions  are 
produced:  (i)  First  runnings  to  105°  C.  containing  ammonical 
liquor  and  first  light  oils;  (2)  second  light  oils  from  105°  to 
210°  C.;  (3)  carbolic  oils  from  210°  C.  to  240°  C.;  (4)  heavy, 
dead,  or  creosote  oils  240°  C.  to  270°  C.,  and  (5)  anthracene 
or  green  oil  above  270°  C.  All  of  these  fractions  are  more  or 
less  contaminated  with  portions  of  the  other  fractions  which  are 
carried  over  or  held  back  mechanically,  and  have  to  be  them- 
selves subjected  to  further  distillation  in  order  to  obtain  purer 
substances.  The  light  oils  are  distilled  for  benzol  and  naphtha; 
the  carbolic  oils  are  treated  to  obtain  carbolic  acid  and  naphtha- 
lene, which  is  largely  found  in  this  distillate;  the  creosote  oils 
also  contain  naphthalene,  for  which  they  are  sometimes  treated; 
and  from  the  green  oil  anthracene  is  separated.  The  residue 
left  in  the  still  is  known  as  coal  tar  pitch  and  is  a  thick,  viscous 
material  while  hot.  It  represents  the  true  binding  base  of  the 
tar,  and,  if  the  tar  is  one  produced  at  a  comparatively  low  tem- 
perature, is  composed  mainly  of  bitumens.  After  cooling  some- 
what it  is  run  out  of  the  still  into  a  smothering  chamber,  and 
after  further  cooling  is  drawn  off,  and  graded  as  soft,  medium, 
or  hard,  according  to  its  condition  when  cold.  The  dead  oils, 
which  are  of  the  least  value  of  any  of  the  fractions,  are  often 
run  back  into  the  still  before  the  pitch  is  drawn  off.  In  this 
case  the  pitch  is  liquid  when  cold.  Besides  the  three  grades 
mentioned  there  are  numerous  intermediate  varieties  which 
have  their  own  particular  use  in  the  trades.  These  pitches  are 
graded  according  to  their  so-called  melting  point.  Liquid  pitch 
is  often  used  as  a  paint  for  wood  and  metal  work  and  for  making 
tarred  or  roofing  paper,  while  the  harder  pitches  are  employed 
as  cements  or  mastics  and  find  their  place  in  the  road  and  pav- 
ing industries  in  competition  with  the  natural  bitumens.  If 
the  coal  tar  has  been  previously  manufactured  at  an  exceed- 
ingly high  temperature,  all  of  the  free  carbon  or  lampblack 
which  was  originally  deposited  in  the  tar  will  be  found  in  the 
pitch.  Its  waterproofing  and  adhesive  properties  will  therefore 


268  DUST   PREVENTIVES    AND    ROAD    BINDERS 

be  lessened  and  any  preparation  containing  this  pitch  as  a 
base  will  be  correspondingly  poor  for  use  as  a  road  binder. 

Naphthalene  is  one  of  the  most  important  constituents  of 
coal  tar  and  is  consequently  recovered  from  the  various  distil- 
lates. When  pure  it  exists  in  shining  white  plate-like  crystals 
which  volatilize  slowly  at  ordinary  temperatures.  It  has  a 
pungent,  camphor-like  odor  and  is  employed  in  the  manu- 
facture of  moth-balls.  Its  most  important  use,  however,  is 
in  the  preparation  of  coal  tar  dyes.  Its  removal  from  the 
tar  is  undoubtedly  of  advantage  in  the  preparation  of  a  road 
binder  as  it  has  none  of  those  qualities  requisite  for  a  good 
material  of  this  nature.  The  same  may  be  said  of  anthracene, 
which  is  probably  the  most  valuable  constituent  of  coal  tar 
and  is,  therefore,  removed  from  the  fractions  in  which  it  is 
found.  It  is  employed  entirely  in  the  preparation  of  alizarine, 
a  valuable  coloring  material. 

In  the  United  States  but  comparatively  few  gas  companies 
make  any  attempt  to  distill  their  crude  tar,  but  sell  it  to  those 
who  make  a  business  of  tar  distilling.  The  tar  is  either  trans- 
ported by  rail  in  large  tank  cars  or  by  water  in  tank  barges. 
The  distiller  stores  his  tars  in  large  iron  tanks  until  ready  for 
use.  The  upright  stills  previously  described  are  seldom  em- 
ployed, but  in  their  place  large  horizontal  cylindrical  stills  often 
holding  as  much  as  25,000  gallons  are  employed.  They  are 
quite  similar  to  the  stills  used  in  the  oil  industry.  It  is  cus- 
tomary to  divide  the  fractions  into  only  two  portions,  the  light 
oils,  having  a  specific  gravity  of  less  than  i.oo,  and  the  heavy 
oils,  having  a  gravity  greater  than  i.oo.  Distillation  is  often 
carried  only  to  the  point  where  a  residue  of  the  desired  con- 
sistency is  obtained.  These  residues  may  be  either  fluid,  semi- 
solid  or  solid  at  ordinary  temperatures.  If  semisolid  or  solid 
they  are  termed  pitch,  and  graded  according  to  their  melting 
points.  Sometimes  distillation  is  carried  to  the  formation  of 
what  would  be  a  hard  pitch  if  allowed  to  cool,  but  while  still  hot 
sufficient  heavy  or  dead  oils  are  run  back  into  the  still  to  produce 
a  pitch  of  any  desired  consistency.  Such  materials  are  called 


TAR   AND   TAR   PRODUCTS  269 

cut-back  products  and  for  road  purposes  are  usually  superior 
to  the  straight  residues,  for  before  running  back  the  dead  oils 
it  is  customary  to  remove  most  of  the  naphthalene  which  they 
contain.  Sometimes  water  gas  tars  and  coal  tars  are  blended 
before  being  distilled,  usually  for  the  purpose  of  controlling  the 
free  carbon  contents  of  the  residue.  The  blowing  of  tar  pitches 
has  also  been  resorted  to  in  the  preparation  of  road  products, 
particularly  in  the  distillation  of  water  gas  tar. 

Dehydrated  Tars.  --  Sometimes  only  dehydrated  tar  is  pre- 
pared for  use  as  a  dust  preventive  and  semipermanent  binder, 
the  idea  being  to  remove  all  water,  ammonium  compounds  and 
some  of  the  light  oils.  A  preparation  of  this  kind  is  to  be  pre- 
ferred to  the  crude  tar,  as  the  absence  of  water  makes  it  easier 
to  handle  when  applied  hot  and  probably  allows  of  a  better 
absorption  of  the  tar  by  the  road  surface.  If  much  water  is 
present  in  the  tar,  it  is  absorbed  by  the  road  material  in  pref- 
erence to  the  tar  and  thus  becomes  to  a  certain  extent  tar 
proof.  As  a  result  the  tar  is  very  likely  to  peel  after  applica- 
tion. Water  in  the  tar  itself  will  also  hasten  disintegration  of 
the  heavy  binding  materials  during  the  course  of  time.  The 
ammoniacal  liquor  may  saponify  some  of  the  oily  products 
which  are  then  capable  of  mixing  with  water  and,  therefore,  apt 
to  be  washed  out.  The  results  of  examination  of  a  dehydrated 
road  tar  suitable  for  cold  applications  are  given  below: 

DEHYDRATED  ROAD  TAR. 

Character Thin,  oily 

Specific  gravity i .  086 

Distillation: 

Water,  per  cent  by  vo o .  o 

First  light  oils,  to  1 10°  C 7.5 

Second  light  oils  no°-i7o°  C.,  per  cent  by  vol 10.5 

Heavy  oils,  170°— 270°  C.,  per  cent  by  vol 42.0 

Pitch  residue  (by  difference),  per  cent  by  vol 40.0 

100.  o 
Pitch  residue  (per  cent  by  weight) 42.0 

Free  carbon o .  66 

Remarks.  —  None  of  the  distillates  contained  more  than  a  trace  of  precipitated 
naphthalene  when  cold.     The  pitch  showed  a  lustrous  fracture. 


2/0 


DUST   PREVENTIVES  AND    ROAD   BINDERS 


From  the  low  specific  gravity  and  free  carbon  contents  as 
well  as  the  absence  of  appreciable  quantities  of  naphthalene  it 
is  evident  that  this  is  a  dehydrated  water  gas  tar.  Its  superiority 
for  road  purposes  over  the  crude  tar  described  on  page  249  is 
not  only  due  to  its  lack  of  water,  but  also  to  the  presence  of  a 
larger  amount  of  pitch.  Such  a  material  will  prove  very  suitable 
as  a  dust  preventive  and  temporary  binder  when  employed  in 
the  surface  treatment  of  macadam  roads. 

Residual  Tars.  —  Residual  tars,  as  has  been  stated,  are  those 
from  which  the  lighter  products  have  been  removed  by  dis- 
tillation. They  may  be  of  any  consistency  from  very  fluid  to 
solid.  Only  the  fluid  and  semisolid  tar  pitches  are  employed 
in  road  treatment,  as  the  solid  varieties  are  too  brittle  to  prove 
satisfactory.  The  properties  of  three  typical  residual  road  tars, 
the  first  two  of  which  are  trade  products,  are  given  in  the  follow- 
ing table: 

RESIDUAL    ROAD    TARS. 


i 

2 

3 

Character  

Viscous, 

Semisolid 

Semisolid 

Specific  gravity,  25°/25°  C  . 

Smooth, 
i  .  177 

Fairly  Smooth. 

1.248 

Fairly  Smooth. 

I  .  2  3Q 

Melting  point    degrees  C 

Fluid 

26° 

^oy 

20° 

Distillation: 
Water               

o.o 

o  o 

o  o 

First  light  oils  to  no°C.,  per  cent 
by  vol  .  

Trace 

.0 

o  o 

Second  light  oils   iio°-i7o°C.,   per 
cent  by  vol 

12    8 

I     2 

Heavy  oils    i7o°-27o°  C.,    per   cent 
bv  vol    

47  •  6 

2O    2 

•7-2      T 

Pitch  residue  (by  difference),  per  cent 
by  vol                                

•3Q      6 

78  6 

66  5 

Pitch  residue  (per  cent  by  weight)  .  . 
Free  carbon          .        

100.  0 
I  I  .  2 

IOO.O 

82.3 

2T.    Q  C 

IOO.O 

71.0 

Remarks.  —  In  sample  i  the  light  oils  were  free  from  precipitated  naphthalene 
when  cold,  while  the  dead  oils  showed  one-third  their  volume  of  this  constituent. 
The  fracture  of  the  pitch  residue  was  fairly  lustrous.  In  No.  2  the  light  oils 
showed  about  one-half  their  volume  precipitated  naphthalene  and  the  heavy  oils 
about  two-fifths.  In  No.  3  the  heavy  oils  showed  two-thirds  their  volume  pre- 
cipitated naphthalene.  The  pitch  residue  for  both  2  and  3  showed  a  rather  dull 
fracture. 


TAR   AND   TAR   PRODUCTS  271 

Upon  comparing  these  residual  tars  with  the  crude  tars  on 
pages  237  and  241,  it  will  be  seen  that  the  water  and  first  light  oils 
of  the  latter  are  absent  and  that  with  the  exception  of  No.  i 
the  percentage  of  second  light  oils  is  very  much  lower.  The 
specific  gravity  of  a  residual  tar  is  not  necessarily  greater  than 
other  crude  tars,  although  it  is  higher  than  the  original  crude  tar 
from  which  it  was  produced.  The  free  carbon  content  of  the 
residue  is  also  greater  than  of  the  original  crude  material. 

As  compared  with  the  other  two  tars,  No.  i  is  a  much  more 
fluid  residue,  as  shown  by  the  relative  proportion  of  oils  and 
pitch.  The  presence  of  a  greater  amount  of  second  light  oils 
shows  either  that  distillation  has  not  been  carried  so  far  as  in 
the  other  two  tars  or  that  it  is  a  cut-back  product.  The  latter 
fact  might  be  indicated  by  the  large  amount  of  heavy  oils,  which 
is  abnormal  for  a  plain  residual  coal  tar.  Such  a  product  could, 
however,  have  been  prepared  by  distilling  a  mixture  of  coal  tar 
and  water  gas  tar  and  this  would  seem  to  be  the  most  probable 
assumption,  in  view  of  the  rather  high  percentage  of  light  oils 
which  are  free  from  naphthalene  and  the  presence  of  consider- 
able quantities  of  naphthalene  in  the  heavy  oils.  Had  no  light 
oils  been  present  and  the  heavy  oils  been  free  from  naphthalene, 
it  would  have  shown  the  properties  of  a  true  cut-back  coal  tar, 
the  percentage  of  free  carbon  eliminating  any  possibility  of  its 
being  a  straight  residual  water  gas  tar.  This  tar  does  not 
contain  an  excessive  amount  of  free  carbon  and  when  heated 
is  suitable  for  use  as  a  semipermanent  binder  in  the  surface 
treatment  of  macadam  roads.  Owing  to  its  fluidity  it  is  not 
suited  for  macadam  construction. 

Tar  No.  2  might  be  employed  in  construction  work  but  con- 
tains more  free  carbon  than  is  desirable  and  too  small  a  proportion 
of  heavy  oils  to  the  pitch  residue  for  a  material  of  such  a  low 
melting  point.  A  tar  of  this  nature  is  apt  to  become  brittle 
and  dead  quite  rapidly  after  application. 

Tar  No.  3  is  somewhat  better  adapted  for  road  work  but  con- 
tains what  should  probably  be  the  maximum  allowable  limit  of 
free  carbon  and  decidedly  more  naphthalene  than  is  to  be 


2/2  DUST   PREVENTIVES   AND    ROAD   BINDERS 

desired.  On  the  whole,  however,  it  may  be  considered  as  a 
fair  road  binder,  the  proportion  of  heavy  oils  to  pitch  residue 
being  about  normal  for  a  tar  of  its  consistency.  This  material 
was  prepared  by  distilling  a  mixture  of  crude  high  carbon  coal 
tar  and  water  gas  tar  for  the  purpose  of  reducing  the  free  carbon 
to  at  least  20  per  cent.  From  the  analysis  of  a  material  of  this 
nature  it  is  rather  difficult  to  tell  whether  it  is  a  simple  residual 
medium  temperature  coal  tar  or  a  blended  tar,  but  this  is  not  a 
very  important  matter,  as  a  knowledge  of  the  properties  of  the 
tar  itself  is  of  more  interest  to  the  road  engineer  than  the  method 
of  manufacture.  From  the  experience  of  the  author  it  would 
seem  quite  probable  that  originally  undesirable  coal  tars  may 
be  blended  with  water  gas  tars  to  produce  fairly  satisfactory 
residual  products. 

Blown  Tars.  —  Quite  recently  residual  tars  which  have  been 
blown  during  the  process  of  distillation  in  a  manner  similar  to 
that  described  under  blown  oils  (see  page  158)  have  appeared  on 
the  market,  and  in  some  respects  would  seem  to  be  preferable 
to  the  unblown  tars.  Contrary  to  what  might  be  expected 
from  the  effect  of  blowing  air  through  hot  oils,  the  ductility  of 
tars  does  not  seem  to  be  injured  by  this  process,  but  rather 
increased.  Just  what  chemical  reactions  take  place  is  not 
known,  but  they  are  probably  similar  in  character  to  those 
which  occur  upon  blowing  oils,  although  in  this  case  the  aro- 
matic compounds  are  condensed  and  oxidized  in  place  of  the 
polymethylenes.  One  effect  of  blowing  seems  to  be  a  raising 
of  the  boiling  points  of  some  of  the  hydrocarbons,  which  increases 
the  pitch  contents.  This  is  indicated  by  the  results,  shown 
in  the  following  table,  of  an  examination  of  two  residual  water 
gas  tars  of  approximately  the  same  consistency,  one  of  which 
was'  blown  during  distillation.  The  two  tars  referred  to  are 
numbered  2  and  3,  No.  2  being  the  blown  product.  No.  i  is 
also  a  blown  product  but  of  a  more  fluid  nature. 

In  all  of  these  products  the  low  carbon  content  and  lustrous 
fracture  of  the  pitch  residue  show  that  they  have  been  pre- 
pared from  water  gas  tars.  They  are  all  suitable  for  road 


TAR  AND  TAR  PRODUCTS 


2/3 


COMPARISON  OF  BLOWN  AND  STRAIGHT  RESIDUAL 
WATER  GAS  TAR. 


Blown. 

Plain 
Residual. 

i 

2 

3 

Character        .        

Smooth, 
Viscous. 
1.158 

0.0 

•4 
•  7 
33-2 

65-7 

Smooth, 
Very  Viscous. 
1.  167 

0.0 

°-5 
3-o 

29.0 

67-5 

Smooth, 
Very  Viscous, 
i  .  165 

0.0 
0.0 

6-3 
5i-9 

41.8 

Specific  gravity  

Distillation: 
Water,  per  cent  by  vol  

First  light  oils  to  110°  C.,  per  cent  by 
vol  

Second  light  oils,   no°-i7o°C.,  per 
cent  by  vol 

Heavy   oils,    j.'jo0-2'jo°  C.,  per  cent 
by  vol         .                    ... 

Pitch  residue  (by  difference),  per  cent 
by  vol  

Pitch  residue  (per  cent  by  weight)  .  . 
Free  carbon 

100.  0 

69.4 

*>*s 

100.  0 

71.2 
2.09 

100.  0 

45-4 

2-53% 

Remarks. — None  of  the  distillates  showed  more  than  a  trace  of  precipitated 
naphthalene  when  cold  and  all  of  the  pitch  residues  had  a  lustrous  fracture. 

construction,  but  No.  3  has  an  almost  abnormally  low  pitch 
residue,  which  is  characteristic  of  straight  distilled  water  gas 
tars.  This  property  has  been  greatly  modified  by  blowing,  as 
shown  by  Nos.  i  and  2.  Blown  tars  have  not,  however,  been 
in  use  for  a  sufficiently  long  time  to  warrant  any  very  definite 
assertion  as  to  their  lasting  qualities. 

Summary  and  Conclusions.  —  In  this  chapter  the  character- 
istics of  various  tars  with  relation  to  the  treatment  of  roads 
have  been  discussed  at  some  length,  and  the  methods  of  pre- 
paring them  described.  Our  present  knowledge  of  the  effect  of 
composition  upon  the  physical  properties  of  tars  is  somewhat 
limited  and  much  yet  remains  to  be  investigated.  The  fore- 
going should,  however,  serve  as  a  working  basis  for  future  inves- 
tigations and  will,  it  is  hoped,  prove  of  some  service  in  enabling 
the  road  engineer  to  form  a  correct  idea  of  the  properties  most 


2/4  DUST   PREVENTIVES   AND    ROAD   BINDERS 

essential  in  tars  that  are  to  be  used  as  dust  preventives  and 
road  binders.  It  is  probable  that  the  near  future  will  see  an 
immense  amount  of  road  work  in  which  tar  is  employed  as  a 
binding  medium.  The  possible  available  supply  of  tar  in  this 
country  is  quite  as  great  as  that  of  good  road  oils  and  there 
seems  to  be  no  reason  why  both  classes  of  binders  should  not 
continue  to  compete  on  an  equal  footing.  As  compared  with 
good  road  oils  the  good  road  tars  may  perhaps  tend  to  weather 
a  little  faster  and  are  certainly  somewhat  more  susceptible  to 
temperature  changes.  They  are  on  the  other  hand  much  more 
powerful  binders  than  oils  on  a  basis  of  like  consistency  and 
should  if  properly  selected  and  used  give  fully  as  satisfactory 
results. 


CHAPTER  XII. 

THE  APPLICATION  OF  TAR  AND   CONSTRUCTION   OF 
BITUMINOUS  MACADAM. 

THE  earliest  recorded  attempt  to  use  tar  as  a  road  binder  was 
made  at  Nottingham,  England,  about  1840,  in  the  construc- 
tion of  a  tar  macadam  road,  and  soon  after  this  at  Sheffield,  in 
a  similar  manner.  In  1854  its  use  in  this  connection  was  in- 
troduced in  Paris  and  in  1866  in  Knoxville,  Tennessee.  In  1867 
the  application  of  tar  in  the  surface  treatment  of  roads  first  sug- 
gested itself  to  French  engineers  and  from  then  until  1903  a 
number  of  isolated  experiments  were  conducted  along  this  line 
in  France,  England,  Australia,  Italy  and  the  United  States. 
Since  1903  the  subject  has  received  more  general  attention 
and  particularly  during  the  last  few  years.  While  the  sur- 
face treatment  of  roads  with  tar  was  undergoing  a  slow  proc- 
ess of  development,  its  use  in  street  paving  suddenly  came 
into  prominence  in  1871  at  Washington,  D.  C.,  fostered  under 
patents  granted  to  Snow  and  Davis.  In  these  patents  sulphuric 
acid  was  employed  as  a  hardening  agent,  and  a  variety  of  ma- 
terials, such  as  sawdust,  ashes,  etc.,  were  used  in  the  mixture. 
During  the  next  seven  years  about  750,000  square  yards  of  tar 
concrete  pavement  were  laid  in  this  city.  Owing  to  the  fact 
that  but  little  attention  was  paid  to  the  character  of  the  tar 
employed,  and  very  probably  to  the  use  of  sulphuric  acid,  many 
of  these  pavements  failed  within  a  few  years  and  had  to  be 
relaid.  These  failures  proved  to  be  a  severe  setback  to  the 
use  of  tar  as  a  paving  material  in  this  country,  as  the  work  at 
Washington  attracted  quite  general  attention.  Incidentally 
they  also  proved  a  boon  to  those  interested  in  the  asphalt  in- 
dustry, who  by  discrediting  tar  advertised  their  own  products 
to  advantage.  While  the  author  does  not  wish  to  compare 

275 


2/6  DUST  PREVENTIVES   AND   ROAD   BINDERS 

these  two  substances  as  paving  materials,  he  believes  that  the 
general  discredit  thrown  upon  tar  because  of  its  early  failures 
is  greatly  retarding  its  use  in  this  country  in  modern  road  con- 
struction. In  spite  of  its  many  failures  and  the  fact  that  the 
work  at  Washington  was  done  so  long  ago  that  since  then  many 
asphalt  pavements  have  been  laid,  worn  out  and  relaid  a  num- 
ber of  times,  a  few  of  the  original  tar  concrete  surfaces  still 
remain  intact  as  a  witness  to  the  possibilities  of  this  material. 
Quite  recently  a  number  of  sections  from  one  of  these  pave- 
ments which  had  been  down  for  over  34  years  were  cut  out 
under  the  author's  supervision,  for  the  purpose  of  making  an 
examination.  Shortly  after  completion  this  pavement,  with 
all  of  the  other  tar  concretes,  was  covered  with  a  course  of 
asphalt  topping  which  has,  however,  long  since  worn  away, 
except  near  the  gutters,  thus  leaving  the  original  tar  pave- 
ment exposed.  The  mineral  aggregate  was  found  to  be  exceed- 
ingly well  bonded  and  the  binder  while  hard  was  by  no  means 
dead,  a  strong  odor  of  coal  tar  being  given  off  by  the  freshly 
turned  sections.  A  sawed  section  of  this  pavement  is  shown 


FIG.  24.    Section  of  Old  Coal-tar  Pavement  laid  at  Washington,  D.  C., 
in  1873.     Surface  in  good  condition  in  1909. 

in  Fig.  24.  The  quantity  of  bitumen  present  amounted  to  about 
6  per  cent  of  the  whole  and, the  mineral  aggregate  showed  the 
following  characteristics  for  three  sections  which  were  examined. 


TAR   AND   CONSTRUCTION   OF   BITUMINOUS    MACADAM 

OLD  COAL  TAR  PAVEMENT. 
WASHINGTON,  D.C. 


Sample   No  

I 

2 

3 

Per  ce 
Miner 
Ret 
Pas 

Per  ce 

nt  bitum 
al  aggreg 
lined  on 
,ing    i  in 

i 

i 

8m 

10 

20 

3° 
40 

5° 
80 

100 
200 

nt  of  voi( 

zn  in  p 
ate: 
i  inch 
ch  reta 

sh 

aveme 

screen 
ned  o 

nt 

6.8% 

2.2% 

7-3 
26.7 
18.7 

*5-* 

4-2 
6.6 
3-3 

6.2% 

1.3% 

5-2 

29.6 

34.4 

I2-5 

2.7 

3-3 

2.  I 

2.8 

•9 
1.8 
0.6 

I.O 
2.0 

6.0% 

2.8% 

3-6 
16.6 
21.4 
16.7 
5-i 
7-4 

4-7 
4.6 
1.4 
4.1 

i-3 

2.5 
7.8 

n    f  inch  

1  "     . 

i  "     

8  mesh  

10                 
20                 

3°           

40 

4                            !> 

£     :::::::'. 

3-6 

2.7 
0.9 

8.7 

100         

2OO                              ,  .    ) 

Is                                    

IOO.O 

17.0 

IOO.O 
I8.5 

IOO.O 

15.0 

These  results  are  of  interest  as  showing  a  type  of  road  or 
pavement  in  which  tar  has  proved  a  very  satisfactory  binder 
and  it  is  only  reasonable  to  suppose  that  with  proper  care  in 
selection  and  application  these  roads  can  be  duplicated.  Un- 
fortunately no  data  are  to  be  had  in  regard  to  the  physical  and 
chemical  properties  of  the  binder  which  was  employed  in  this 
early  work  and  any  examination  of  this  binder  as  it  exists  to-day 
is  of  little  value  for  the  reason  that  alterations  have  taken  place 
during  the  course  of  time  which  mask  its  original  character- 
istics and  make  it  extremely  difficult  to  isolate  the  bitumen 
even  as  it  exists  at  present  in  the  pavement. 

In  England,  France  and  Canada,  the  use  of  coal  tar  in  the 
treatment  and  construction  of  roads  has  found  much  more  favor 
than  in  the  United  States,  and  the  two  first  mentioned  countries 
are  considerably  in  advance  of  us  both  in  regard  to  total  mileage 
of  tar  treated  roads  and  in  methods  of  application.  To  a  great 
extent  we  have  so  far  only  succeeded  in  repeating  their  early 
and  more  unsuccessful  attempts,  and  while  there  is  much  yet  to 


2/8  DUST   PREVENTIVES    AND    ROAD    BINDERS 

be  learned  as  to  the  quality  of  tar  which  will  produce  the  most 
economical  and  satisfactory  results  under  given  conditions,  we 
should  at  least  profit  by  their  improvements  in  methods  of 
application,  which  up  to  the  present  time  have  not  been  generally 
employed  in  this  country. 

Unlike  oils,  tars  have  not  so  far  appeared  to  advantage  in 
the  treatment  of  any  but  broken  stone  roads,  and  their  use  in 
this  connection  only  will  here  be  described.  It  is  quite  possible 
that  under  favorable  conditions  both  earth  and  gravel  roads 
may  be  successfully  treated  with  these  materials  but  so  little 
work  of  this  nature  has  been  tried  that  at  present  it  is  impossible 
to  make  any  definite  assertion  in  regard  to  the  matter.  Tar 
may  be  employed  either  in  the  surface  treatment  of  old  macadam 
roads  or  in  the  construction  of  new  roads.  In  the  former  case, 
it  may  be  used  either  as  a  dust  layer  and  temporary  binder  or 
as  a  semipermanent  binder,  depending  largely  upon  its  con- 
sistency. In  road  construction  it  of  course  plays  the  part  of 
a  permanent  binder,  and  may  be  employed  in  a  variety  of  ways, 
the  two  most  common  being  known  as  the  penetration  method 
and  the  mixing  method.  In  the  first  case  application  may  be 
made  either  by  hand  or  by  mechanical  spreaders  and  in  the  latter 
either  hand  or  mechanical  mixing  may  be  resorted  to.  A  third 
method  of  construction,  known  as  the  Gladwell  system,  has  also 
been  employed  to  some  extent.  All  of  these  methods  are  de- 
scribed below.  It  may  be  stated  that  the  methods  of  construc- 
tion are  equally  applicable  to  oils  and  for  this  reason  no  details 
of  the  construction  of  oil  macadam  roads  were  included  in 
Chapter  X.  A  number  of  patents  covering  methods  of  con- 
structing bituminous  macadam  have  been  issued  by  the  United 
States  Patent  Office  and  some  are  now  being  adjudicated  which 
if  upheld  may  greatly  influence  the  character  of  future  work  of 
this  nature.  In  the  following  descriptions  of  methods  it  has 
been  the  aim  of  the  author  to  include  all  points  which  are  con- 
sidered as  best  practice,  without  reference  to  any  one  individual 
patent. 

Surface  Application  of  the  Lighter  Tars.  —  The  term  lighter 


TAR  AND   CONSTRUCTION  OF   BITUMINOUS   MACADAM     2/9 

tars  as  here  used  refers  to  both  crude  and  refined  products 
which  are  sufficiently  fluid  at  ordinary  temperatures  to  be  ap- 
plied by  means  of  a  common  sprinkling  cart.  Most  crude  coal 
tars  are  too  viscous  for  this  purpose,  but  crude  water  gas  tar 
may  often  be  so  employed  to  advantage.  This  material  can  be 
obtained  for  about  3  cents  a  gallon,  and  when  applied  at-  the  rate 
of  .3  gallon  per  square  yard  on  an  ordinary  macadam  will  success- 
fully lay  the  dust  for  some  time.  The  number  of  applications 
required  during  a  season  will  of  course  depend  upon  a  number  of 
conditions,  but  under  ordinary  circumstances  a  comparatively 
few  will  suffice.  This  material  is  quite  readily  absorbed  by  the 
road  and  contains  a  sufficient  amount  of  pitch  to  reduce  dust 
formation  to  a  considerable  extent.  It  has  a  rather  objection- 
able gassy  odor,  which,  however,  soon  disappears.  When  used 
on  roads  carrying  a  great  amount  of  fine  material,  it  is  sometimes 
necessary  to  apply  more  than  .3  gallon  per  square  yard.  In  a 
case  of  this  sort  the  tar  does  not  bind  the  dust  down  firmly  to 
the  underlying  surface,  but  it  holds  the  particles  well  together 
and  keeps  them  from  being  raised  by  passing  vehicles  or  winds. 
Under  the  action  of  traffic  this  loose  or  floating  surface  is  alter- 
nately compacted  and  broken  up,  but  does  not  form  a  dis- 
agreeable mud.  During  rainy  weather,  in  fact,  it  has  been 
known  to  produce  a  compact,  uniform  surface  which  appears  to 
advantage  in  comparison  with  the  surface  in  dry  weather.  In 
localities  where  it  can  be  readily  obtained  with  but  little  cost 
for  transportation,  it  can  undoubtedly  be  used  to  advantage,  and 
in  many  cases  should  successfully  compete  with  other  temporary 
binders. 

Mixtures  of  crude  water  gas  tar  and  crude  coal  tar  propor- 
tioned so  as  to  obtain  a  maximum  amount  of  pitch  base  with  the 
minimum  degree  of  fluidity  requisite  for  cold  application  pro- 
duce more  lasting  results,  but  by  far  the  best  of  this  type  of 
binders  are  the  partially  refined  water  gas  tars  from  which  all 
water  and  part  of  their  light  oils  have  been  removed,  or  else  the 
partially  refined  coal  tars  which  have  been  cut  with  light  oils 
until  sufficiently  fluid  for  this  purpose.  Such  tars  are  capable  of 


280  DUST   PREVENTIVES   AND    ROAD    BINDERS 

developing  considerable  binding  value  after  application  and  at  the 
same  time  act  as  excellent  dust  preventives.  If  a  large  amount 
of  dust  is  present  on  the  road  it  should  be  removed  before 
application,  but  under  ordinary  conditions  this  is  not  necessary. 
If  the  road  is  fairly  free  from  dust  before  application,  a  single 
treatment  with  such  tars  should  render  it  practically  dustless 
for  a  season  unless  the  traffic  is  excessive.  They  will  not  prevent 
raveling,  however,  under  heavy  traffic,  as  their  binding  value  is 
not  sufficiently  great.  The  cost  of  treatment  should  amount  to 
not  over  three  cents  per  square  yard  per  annum. 

Surface  Application  of  the  Heavier  Tars.  —  When  crude  tars 
are  not  sufficiently  fluid  to  apply  cold,  it  is  poor  economy  to 
attempt  to  use  them,  as  the  cost  involved  in  heating  and  handling 
is  not  commensurate  with  the  results  obtained,  for  reasons 
mentioned  in  the  preceding  chapter.  The  heavier  tars  as  here 
considered  will  include  only  dehydrated  or  refined  tars  of  suffi- 
cient fluidity  to  pour  from  the  bung  of  a  barrel,  but  too  viscous 
to  be  applied  cold  to  the  road  surface.  Harder  materials  than 
this  will  not  be  found  satisfactory  for  the  surface  treatment  of 
old  roads,  owing  to  their  inability  to  penetrate  the  road.  Crude 
tars  have  sometimes  been  boiled  in  kettles  at  the  roadside  until 
all  water  has  been  driven  off  and  the  product  has  attained  con- 
siderable viscosity.  This  is  a  slow  and  tedious  operation,  however, 
and  there  is  much  danger  of  the  tar  frothing  up,  boiling  over  and 
catching  fire  if  the  temperature  is  raised  above  90°  C.  while  the 
water  is  being  driven  off. 

Experience  has  shown  that  in  order  to  get  the  best  results 
from  applications  of  the  heavier  tars  the  road  should  be  free 
from  dust,  perfectly  dry,  and  comparatively  warm.  If  dust  and 
other  fine  material  are  present  the  tar  will  not  be  properly 
absorbed  by  the  surface  and,  owing  to  a  lack  of  bond,  will  soon 
peel  and  be  removed  by  traffic.  For  this  reason  it  can  be 
applied  successfully  to  hard  surfaces  only,  such  as  are  presented 
by  well- swept  macadam  or  cement  concrete  roads.  The 
presence  of  moisture  will  also  prevent  the  tar  from  penetrat- 
ing the  road,  and  as  a  cold  surface  will  chill  and  stiffen  the 


TAR   AND   CONSTRUCTION    OF   BITUMINOUS   MACADAM     28 1 

material  it  is  necessary  that  all  applications  be  made  in  dry, 
warm  weather.  Before  applying  the  tar  the  road  should  be 
repaired  where  necessary,  in  order  to  secure  as  smooth  and  even 
a  surface  as  possible.  If  ruts  and  hollows  are  present,  the 
tarred  road  will  not  only  present  a  poor  appearance,  but  accumu- 
lations of  water  in  these  depressions  will  produce  rapid  disinte- 
gration of  the  tar,  followed  by  its  complete  removal  under  the 
action  of  traffic.  It  is  desirable  that  repairs  be  made  for  some 
time  previous  to  the  tar  application  in  order  to  obtain  a  well- 
bonded  and  consolidated  surface  to  start  with,  for  it  has  been 
found  that  fresh  patches  which  have  been  tarred  are  not  unlikely 
to  ravel  if  traffic  is  at  all  heavy. 

The  primitive  method  of  application  which  has  been  largely 
employed  in  this  country  up  to  the  present  time,  and  formerly  in 
France  and  England,  is  as  follows:  The  road  surface  is  first 
thoroughly  swept  in  order  to  remove  all  dust.  The  hot  tar  is 
then  spread  on  and  thoroughly  broomed  in.  The  road  should, 
if  possible,  be  closed  to  traffic  and  the  tar  allowed  to  remain 
untouched  for  about  twelve  hours  in  order  to  allow  it  to  soak  in. 
At  the  end  of  this  time,  or  sooner  if  necessary,  a  coat  of  clean 
sand  or  stone  chips  should  be  applied  to  absorb  the  excess  of  tar, 
and  the  surface  should  then  be  rolled  several  times  to  bring  it 
to  proper  condition  quickly.  The  preliminary  sweeping  of  the 
road  is  sometimes  done  by  hand,  but  an  ordinary  mechanical 
street  sweeper  is  often  to  be  preferred,  as  it  performs  the  work 
more  economically  and  with  greater  expedition.  The  tar  is 
heated  in  an  open  kettle  preferably  mounted  on  wheels  and 
fitted  with  a  portable  fire  box.  It  is  usually  brought  to  about 
100°  C.  before  being  spread  upon  the  road,  although  a  lower 
temperature  is  sometimes  sufficient,  and,  if  the  kettle  is  of 
the  type  described  above,  the  tar  may  be  run  out  upon  the 
road  as  required  by  means  of  a  hose,  the  kettle  being  kept 
just  in  advance  of  the  work,  as  shown  in  Fig.  25.  By 
using  two  kettles  the  process  may  be  made  continuous,  one 
being  charged  and  heated  while  the  other  is  in  use.  Kettles 
holding  easily  9  barrels,  or  about  450  gallons,  of  tar  without 


282  DUST   PREVENTIVES    AND    ROAD    BINDERS 


FIG.  25.    Application  of  Tar  to  Macadam  Road  Surface. 


TAR   AND    CONSTRUCTION    OF   BITUMINOUS    MACADAM     283 

danger  of  spilling  over,  and  mounted  on  comparatively  large 
wheels,  are  to  be  preferred  for  this  purpose  when  long  sections 
of  road  are  to  be  treated.  Fig.  26  shows  a  type  of  kettle  suitable 
for  this  work,  and  method  of  loading  same.  This  kettle  has  a  low 
partition  in  the  center.  Cold  tar  is  charged  into  the  section 
over  the  fire  box  and  as  it  becomes  heated  flows  over  into  the 
draw-off  section  so  that  the  operation  of  loading  and  unloading 
may  be  made  continuous.  By  this  means  cold  tar  is  prevented 
from  reaching  the  draw-off.  When  it  is  impossible  to  obtain 
kettles  mounted  on  wheels,  a  number  of  smaller  ones  holding 
about  two  barrels  each  are  sometimes  used.  These  kettles  are 
moved  along  the  side  of  the  road  as  the  work  progresses 
and  the  hot  tar  is  drawn  off  into  flat-nosed  watering-pots,  hods, 
or  ladles,  and  spread  by  hand.  In  either  case  it  is  necessary 
to  have  the  hot  tar  well  broomed  into  the  surface  to  obtain  a 
smooth  and  uniform  coat.  This  spreading  is  usually  done  by 
laborers  with  stiff,  long-handled  brooms,  similar  to  those  used 
in  street  sweeping,  who  follow  the  tar  spreaders  and  broom 
carefully  every  portion  of  road  surface.  The  excess  of  tar  is 
thus  pushed  ahead  and  can  be  used  for  covering  fresh  sur- 
faces. 

After  the  tar  has  been  spread  it  should  be  allowed  to  remain 
undisturbed  for  at  least  twelve  hours,  as  has  been  stated.  In 
cases,  however,  where  it  is  impossible  to  keep  traffic  away  for 
this  length  of  time,  one  of  two  methods  may  be  followed. 
Either  one-half  the  width  of  the  road  may  be  covered  at  one 
time,  thus  allowing  the  other  half  to  be  open  while  the  first  is 
drying,  or  a  coat  of  sand  or  fine  stone  chips  may  be  applied  at 
once  in  sufficient  quantity  to  prevent  the  tar  from  sticking  to 
the  wheels  of  vehicles.  If  the  first  method  is  followed  more 
lasting  results  are  to  be  expected,  but  unless  considerable  care 
is  taken,  the  finished  road  will  present  a  poor  appearance,  owing 
to  the  overlapping  of  the  second  application  on  the  first,  which 
produces  a  seam  along  the  center  of  the  road.  More  time  will 
also  be  consumed,  as  the  length  of  the  road  will  have  to  be  gone 
over  twice.  If  the  second  method  is  employed,  there  is  danger 


284  DUST   PREVENTIVES   AND    ROAD   BINDERS 


TAR  AND   CONSTRUCTION    OF  BITUMINOUS   MACADAM     285 

of  the  tar  being  absorbed  by  the  loose  material  rather  than  by 
the  road  proper,  and  this  will  result  in  a  lack  of  sufficient  bond. 
If  the  tar  is  allowed  to  remain  undisturbed  for  about  twelve 
hours  it  will,  under  ordinary  conditions,  be  fairly  well  absorbed 
by  the  road,  and  then  only  enough  top  dressing  need  be  applied 
to  take  up  the  surplus.  Either  clean  coarse  sand  or  one-half 
inch  hard  stone  chips  are  to  be  preferred  as  a  top  course,  as  these 
afford  a  harder  and  better  wearing  surface  than  most  other 
materials,  such  as  road  dust  and  gravel.  It  is  customary  to 
finish  the  road  by  rolling  this  fine  material  into  the  tar,  but  when 
only  a  light  coat  is  applied  the  rolling  may  be  unnecessary,  as 
the  action  of  traffic  will  in  a  short  time  produce  the  same 
result. 

If  the  tar  does  not  contain  much  heavy  binding  material  and 
it  is  found  necessary  to  patch  the  road  during  tarring,  the  addi- 
tion of  heated  pitch,  of  a  consistency  similar  to  that  used  in 
road  construction,  to  these  patches  will  better  tend  to  consoli- 
date them  and  prevent  them  from  being  torn  up  by  passing 
vehicles. 

A  good  tar  from  which  the  ammoniacal  water,  light  oils, 
naphthalene,  etc.,  have  been  removed  and  the  pitch  diluted  with 
a  sufficient  amount  of  the  heavier  tar  oils  to  give  it  proper 
consistency  will  produce  the  best  and  most  lasting  results. 
There  are  a  number  of  preparations  now  on  the  market  which,  it 
is  claimed,  have  these  qualities.  They  should,  however,  always 
be  examined  to  see  if  they  are  really  what  they  are  claimed  to 
be,  as  the  author  has  examined  different  lots  of  some  of  these 
preparations  and  found  essential  and  inexcusable  differences  to 
exist. 

Owing  to  the  considerable  expense  and  time  consumed  in 
applying  the  tar  from  kettles,  it  is  advisable  to  make  use  of  a 
sprinkling  tank.  Oil  sprinklers  such  as  described  in  Chapter  X 
have  been  employed  to  advantage  for  this  purpose.  Mechanical 
devices  for  applying  the  tar  under  pressure  have  proven  most 
satisfactory  and  are  now  beginning  to  be  adopted  in  this  country. 
France  and  England  stand  foremost  in  the  production  of  tar 


286  DUST   PREVENTIVES   AND    ROAD   BINDERS 

% 

spraying  machines,  having  passed  through  the  hand  spreading 
method  some  time  ago. 

If  the  ordinary  sprinkler  is  employed  it  will  be  found  neces- 
sary to  broom  the  tar  into  the  road  surface.  If,  however,  the 
tar  is  sprayed  under  sufficient  pressure  this  will  not  have  to  be 
done. 

In  France  a  specially  constructed  sprinkler  has  been  used  with 
some  success,  which  can  be  manipulated  by  three  men,  and 
which,  it  is  stated,  will  cover  3000  square  meters  (3  588  yards)  of 
ordinary  roadway  per  day.  Tar  is  pumped  into  a  reservoir, 
and,  after  being  heated  by  petroleum  in  a  manner  similar  to  that 
employed  in  heating  the  boiler  of  a  steam-motor  car,  is  sprayed 
upon  the  road  by  means  of  compressed  air  contained  in  an 
adjoining  reservoir  under  a  pressure  of  5  kilograms  per  square 
centimeter.  If  the  road  is  first  thoroughly  swept  and  all 
remaining  dust  removed  by  means  of  a  vacuum  cleaner,  the  tar 
is  expelled  with  sufficient  force  to  penetrate  well  into  the  mac- 
adam, and  therefore  does  not  require  brooming.  A  light  top  dress- 
ing of  sand  should  afterwards  be  applied  to  the  tarred  surface. 

In  England  the  application  of  tar  by  mechanical  means  has 
been  studied  by  means  of  a  trial  competition,  of  various  ma- 
chines, carried  on  by  a  representative  committee  of  engineers 
and  others  interested  in  road  matters.  Some  exceedingly 
ingenious  devices  were  produced  at  this  contest,  which  give 
promise  of  good  results.  A  number  were  designed  to  carry  on 
the  whole  operation  of  tarring  at  one  passage  of  the  vehicle. 
Some  are  propelled  by  steam  and  so  arranged  that  the  road  is 
first  swept  to  remove  the  dust,  which  is  drawn  up  by  vacuum 
into  a  receptacle  connected  with  the  machine.  The  tar  is 
heated  and  sprayed  upon  the  road  under  considerable  pressure, 
thoroughly  broomed  in,  and  the  dust,  previously  removed,  is 
distributed  over  the  tarred  surface. 

The  first  prize  winner  in  this  contest  is  known  as  the  Aitkins 
pneumatic  tar  sprayer.  During  the  past  year  several  types  of 
these  machines  were  imported  to  this  country  and  proved  very 
successful.  One  of  these  is  shown  in  Fig.  27. 


TAR    AND   CONSTRUCTION   OF   BITUMINOUS    MACADAM     287 


FIG.  27.    Tarspra  Machine. 

Fig.  28  shows  the  details  of  a  similar  machine  described  by 
Aitkin  *  as  follows : 

''Mounted  on  the  frame  A  on  the  vehicle  is  a  supply  tank  B 
to  contain  the  surface-dressing  liquid.  A  receiver  C  for  liquid 
and  air  under  pressure  is  placed  at  the  back  of  the  tank  and  is 
connected  by  an  inlet  pipe  D  with  an  air  or  liquid  pump  E.  The 
pump  is  operated  from  a  road  wheel  F  by  a  chain  wheel  G  fixed  to 
the  road  wheel,  which  drives  through  a  chain  H  to  a  toothed 
pinion  /,  actuating  the  crank  shaft  K  of  the  pump  E.  The 
inlet  L  to  the  pump  is  connected  with  the  supply  tank  B  by  a 
tube  M,  which  is  conveniently  a  flexible  metallic  tube  at  the 
tank  end,  and  a  rose  or  strainer  N  is  fixed  on  the  end.  An  air 
inlet  and  regulating  valve  0  is  provided  on  the  pipe  M  between 
the  supply  tank  and  the  pump  so  that  either  air  or  liquid  may 
be  admitted  to  the  pump,  or  the  proportion  of  liquid  and  addi- 
tional air  may  be  regulated  as  required  for  the  purpose  of  agi- 
tating and  mixing  the  liquid  properly. 

*  U.  S.  Patent  918,490. 


288  DUST   PREVENTIVES   AND    ROAD    BINDERS 


FIG.  28.      Sketch  of  Pneumatic  Tar-Spraying  Machine. 


TAR   AND    CONSTRUCTION   OF   BITUMINOUS   MACADAM     289 

"Feed  pipes  P  leading  from  the  receiver  C  and  provided 
with  cocks  Q  conduct  the  liquid  under  pressure  to  a  distribut- 
ing pipe  R  having  jets  Rf  which  discharge  the  liquid  onto  the 
road.  The  distance  between  the  distributing  pipe  and  the 
surface  level  of  the  road  may,  if  desired,  be  variable  to  suit 
the  varying  pressures  in  the  receiver,  the  condition  of  the  road, 
etc.  A  pressure  gage  and  safety  valve  T  are  provided  on  the 
receiver  C. 

"Preferably  air  is  forced  into  the  receiver  C  from  the  pump 
E  until  the  desired  pressure  of,  say,  50  to  100  pounds  per  square 
inch  is  established  according  to  the  viscosity  of  the  liquid  to 
be  used  and  other  conditions;  the  strainer  N  is  then  introduced 
into  the  tank,  or  connection  otherwise  made  between  the  tank 
B  and  the  pump,  and  liquid  is  forced  into  the  receiver  until  the 
pressure  reaches  the  required  degree,  say,  from  150  to  250 
pounds  per  square  inch. 

"The  apparatus  is  now  ready  for  work  and  by  opening  the 
supply  cocks  Q  to  the  distributor  R,  the  liquid  is  squirted, 
preferably  in  the  form  of  fine  compact  solid  streams,  of,  say,  less 
than  one-eighth  of  an  inch  in  diameter,  so  as  to  be  of  a  penetrat- 
ing character  as  they  are  forced  directly  onto  the  surface  of  the 
road  and  are  also  forced  into  the  binding  material  forming  a 
part  of  the  crust  of  the  metaled  surface  of  the  road.  The 
liquid  is  pumped  into  the  receiver  C  in  a  continuous  flow  and 
the  compressed  air  originally  introduced  *nto  the  receiver  main- 
tains a  uniform  pressure." 

One  of  the  most  common  faults  encountered  in  the  practice 
of  tarring  macadam  road  is  failure  to  remove  all  dust  and  loose 
material  from  the  surface.  Too  much  emphasis  cannot  be  laid 
upon  the  necessity  for  doing  this,  as  the  tar  will  not  penetrate 
through  a  film  of  dust,  and  penetration  is  essential  to  success. 
On  an  old  road  places  may  be  found  where  a  considerable 
amount  of  fine  material  is  caked  to  the  surface.  Such  places 
should  be  scraped  away  until  the  larger  stones  of  the  wearing 
surface  are  visible.  In  fact  the  entire  wearing  course  should  be 
stripped  of  all  fine  material  until  it  shows  a  rather  rough  but 


2QO  DUST   PREVENTIVES    AND    ROAD   BINDERS 

not  uneven  mass  of  large  stones,  thoroughly  bedded  together 
but  presenting  a  considerable  amount  of  surface  voids.  After 
the  tar  is  spread  an  excess  of  stone  chips  may  be  applied  so 
that  upon  rolling  all  of  the  surface  voids  may  be  filled.  The 
chips  thus  become  firmly  bedded  in  the  wearing  course  and,  if 
those  .not  bound  down  by  the  tar  are  swept  from  the  road,  will 
produce  a  firm  smooth  surface. 

In  order  to  facilitate  penetration  of  the  heavier  tars,  espe- 
cially where  it  is  difficult  to  remove  all  dust,  it  will  often  be 
found  advantageous  to  first  give  the  road  a  light  sprinkling 
with  a  thin,  dehydrated  water  gas  tar.  This  material  by  oiling 
the  fine  particles  will  help  carry  the  heavier  bitumen  into  the 
road. 

Macadam  roads  that  are  treated  each  season  with  tar  will  be 
found  to  require  less  material  for  each  succeeding  application. 
If  application  is  made  at  the  proper  rate,  the  cost  of  such  work 
should  for  a  period  of  two  or  more  years  prove  more  economical 
than  ordinary  maintenance  for  a  like  time.  The  surface  treat- 
ment of  tar  constructed  macadam  will  often  prove  of  value  by 
adding  to  the  life  of  the  old  tar  matrix.  This  fact  has  been 
recognized  in  England  for  a  long  time.  Walker  Smith,*  in  a 
recent  treatise  on  tar  macadam,  states  that,  to  his  personal 
knowledge,  "tar  spraying  of  surfaces  has  been  carried  out  for 
the  last  twenty  years  principally  in  tar  macadam  back  streets 
and  tar  macadam  footpaths,  not  as  a  means  of  prevention  of 
dust,  but  in  the  ordinary  way  of  revivification  and  repair  of  a  tar 
macadam  surface." 

*  While  the  repairs  necessary  on  a  macadam  road  are  very 
much  lessened  by  the  application  of  tar,  they  must  not  be 
neglected,  for  once  disintegration  begins  it  spreads  very  rapidly. 
Under  favorable  conditions  a  surface  treated  with  a  heavy  tar 
should  last  at  least  one  year  without  requiring  repairs,  (in 
many  cases,  however,  it  has  been  noticed  that  a  few  months 
after  application  the  tar  disintegrates  and  rapidly  disappears 
under  the  action  of  rain  and  traffic.  JA  slimy  mud  is  formed  in  wet 

*  "Dustless  Roads,  Tar  Macadam."    Griffin  &  Co. 


TAR   AND    CONSTRUCTION    OF   BITUMINOUS    MACADAM      29 1 

weather  which  pulverizes  into  a  very  fine  black  irritating  dust 
in  dry  weather.     In  such  instances  the  fault  would  seem  to  be 
either  in  the  method  of  application  or  in  the  quality  of  tar 
employed.     The  results  described  are  exactly  what  might  be 
predicted  from  the  use  of  a  tar  prepared  at  a  high  temperature 
and  containing  a  large  amount  of  free  carbon  and  other  non- 
binding  material.     It  is  unquestionably  the  use  of  such  products 
that  has  in  many  cases  prejudiced  popular  opinion  against  tar  "7 
as  a  dust  preventive.    /There  is  certainly  one  objection  to  the 
tarred  road  which  in  most  cases  is  well  founded  and  this  is  that     \ 
in  frosty  weather  the  road  is  quite  slippery./   This  fault  may, 
however,  be  somewhat  modified  by  the  character  of  the  top 
dressing  employed,  sand  and  stone  chips  being  preferred  to  other 
materials  as  offering  a  better  purchase  to  the  wheels  of  vehicles      \ 
and  a  better  foothold  to  horses. 

The  amount  of  tar  required  to  treat  a  road  will  depend  upon 
the  fluidity  of  the  material  when  applied  and  the  absorbing 
power  of  the  road.  Soft  rocks,  such  as  limestone  and  dolomite, 
will  take  up  more  tar  than  granite  or  trap  and  will  in  general  give 
better  results,  owing  to  the  greater  penetration  and  consequently^ 
stronger  bond  formed.  (^According  to  conditions  and  method  of 
application,  a  surface  treated  road  will  require  from  .35  to  .70 
gallon  of  tar  per  square  yard  when  application  is  made  by  hand. 
When  applied  by  machine  as  little  as  .21  gallon  has  been  used 
with  good  results  for  a  first  treatment.  In  both  cases  the 
application  of  tar  must  be  repeated  from  time  to  time  but  less 
is  required  at  each  successive  application.  ") 

Decayed  vegetation,  prolonged  rains,  and  frost  are  the  worst 
enemies  of  the  tarred  road.  By  keeping  the  road  comparatively 
free  of  rotting  sticks  and  leaves,  the  first  trouble  may  be  over- 
come but  the  others  are  not  to  be  avoided.  The  alternate 
freezing  and  thawing  of  spring,  as  encountered  in  some  localities, 
is  particularly  injurious  to  a  surface  tarred  road  and  rapid  dis- 
integration of  the  thin  coating  is  apt  to  take  place  even  where 
the  surface  and  subdrainage  are  of  the  best.  In  such  localities 
the  road  tarred  throughout  is  undoubtedly  to  be  preferred  to  the 


DUST   PREVENTIVES   AND   ROAD   BINDERS 

surface  treated  road,  as  the  latter  under  the  most  favorable  cir- 
cumstances is  likely  to  succumb  to  the  attacks  of  winter  and 
early  spring. 

The  cost  of  treatment  for  a  road  surfaced  with  hot  tar  will  of 
course  depend  upon  a  number  of  factors.  In  France  when  done 
by  machine  it  will  average  about  three  cents,  and  when  done  by 
hand  five  cents  per  square  yard.  In  this  country,  where  it  is 
generally  applied  by  hand,  the  cost  is  hardly  ever  less  than  six 
cents  and  in  a  great  many  cases  as  high  as  twelve  cents  and 
more  per  square  yard.  This  is  largely  due  to  the  poor  condition 
of  our  roads  before  treatment,  which  necessitates  the  application 
of  more  tar  and  more  surface  dressing  than  if  they  were  in  good 
condition  in  the  first  place.  In  England  it  is  claimed  that  the 
pneumatic  tar  sprayer  will  apply  the  tar  at  a  cost  of  about  $5 
per  mile  of  eighteen  feet  roadway,  exclusive  of  the  cost  of  the  tar. 
It  is  very  doubtful  if  the  expenditure  of  over  five  cents  per 
square  yard  for  the  surface  treatment  of  any  road  with  tar  will 
prove  good  economy  in  the  long  run.  Resurfacing  or  recon- 
struction with  a  tar  matrix  is  much  the  better  practice,  although 
the  first  cost  is  somewhat  higher.  The  price  of  refined  tar  for 
surface  treatment  will  in  this  country  run  from  five  to  eight 
cents  at  the  present  time. 

Application  of  Tar  to  Cement  Concrete  Road  Surface.  - 
Before  leaving  the  subject  of  surface  treatment,  mention  should 
be  made  of  an  experiment  conducted  by  Mr.  Charles  W.  Ross, 
at  Newton,  Mass.,  in  1908,  in  which  tar  was  used  in  the  treat- 
ment of  a  cement  concrete  road  surface  which  had  begun  to  show 
signs  of  scaling  off  under  the  action  of  traffic.  To  quote  from 
a  paper  by  Mr.  Ross:*  "The  experiment  was  tried  by  putting 
a  coat  of  Tarvia  A,  also  a  preparation  of  coal  tar  just  as  it  was 
taken  from  the  gas  works.  This  was  heated  to  a  temperature  of 
about  1 80  degrees  and  spread  onto  the  surface  of  the  cement, 
swept  down  evenly  with  a  broom  and  then  a  light  coating  of 
stone  screenings  or  fine  screened  gravel  applied,  which  I  think  I 
much  prefer  to  the  stone  screenings. 

*  "  Concrete  Roadways,"  Good  Roads  Magazine,  May,  1909,  p.  142. 


TAR   AND   CONSTRUCTION   OF   BITUMINOUS   MACADAM    293 

"The  surface  has  been  kept  intact  for  over  a  year  and  the  tar 
preparation  on  the  surface  is  in  good  condition  at  the  present 
time." 

Bituminous  Macadam  Construction,  Penetration  Method.  — • 
The  penetration  method  may  be  employed  in  the  construction 
of  oil  macadam  in  the  same  manner  as  for  tar  macadam.  There 
are  a  number  of  variations  to  this  method  as  practiced  by 
different  road  engineers,  but  in  general  it  may  be  described  as 
follows: 

The  roadbed  is  first  graded,  shaped  and  rolled  as  in  ordi- 
nary macadam  work.  A  course  of  number  one  crushed  stone, 
ranging  in  size  from  approximately  one  and  one-quarter  to 
two  and  one-half  inches,  is  laid  loose  to  a  depth  of  five  or 
six  inches,  and  thoroughly  rolled,  sand  or  stone  screenings  being 
applied  in  sufficient  quantity  to  produce  a  firm  sound  surface. 
There  should  be  no  excess  of  fine  material,  however,  and  the  tops 
of  the  large  stone  should  always  be  visible.  With  the  exception 
of  being  somewhat  rough,  this  course  is  practically  a  finished 
road  but  is  intended  only  as  the  foundation  for  the  bituminous 
concrete  which  is  afterwards  formed.  Water  may  be  used  in  the 
construction  of  the  foundation  if  desired,  but  this  is  seldom 
deemed  necessary.  The  filler  of  fine  material  serves  two  pur- 
poses. It  makes  the  foundation  solid  and  cuts  off  the  flow  of 
any  bitumen,  which  is  later  applied,  from  the  base  of  the  road, 
where  it  is  not  needed.  A  somewhat  rough  surface  is  desirable  in 
order  that  the  upper  course  may  key  in.  Any  excess  of  screen- 
ings is,  therefore,  to  be  avoided,  as  the  presence  of  too  much  fine 
material  will  prevent  the  formation  of  a  good  bond  between  the 
two  courses. 

The  second  course  of  crushed  stone,  ranging  in  size  from  one- 
half  inch  to  one  and  one-quarter  inch,  is  laid  on  the  foundation 
course  to  the  depth  of  two  and  one-half  inches  and  well  rolled. 
Where  the  roadstone  is  soft,  larger  sizes  may  sometimes  be 
employed  to  advantage,  as  noted  in  Chapter  I.  A  light  coating 
of  clean  one-half  inch  stone  chips  free  from  dust  is  then  applied 
and  rolled  into  the  surface  which  should,  however,  never  be 


2Q4  DUST   PREVENTIVES   AND   ROAD   BINDERS 

completely  filled.  Tar  or  oil  heated  to  a  considerable  degree 
of  fluidity  is  next  poured  or  sprinkled  over  the  road  at  the 
rate  of  from  one  to  one  and  one-half  gallons  per  square  yard. 
This  is  allowed  to  penetrate  into  the  wearing  surface  and 
should  completely  cover  the  upper  two  inches  of  stone.  Clean 
stone  chips  are  next  applied  and  the  road  again  rolled,  care 
being  taken  not  to  run  the  roller  too  fast  nor  to  reverse 
it  suddenly  on  the  bitumen  coated  surface.  At  this  point  the 
surface  may  wave  somewhat  under  the  roller,  owing  to  the 
at  first  slightly  lubricating  effect  of  the  bitumen.  After 
the  screenings  have  been  rolled,  in  all  surplus  of  fine  material 
is  swept  to  the  sides  of  the  road  for  future  use.  A  seal  or  flush 
coat  of  hot  bitumen  is  then  sprinkled  or  painted  on  the  sur- 
face at  the  rate  of  from  0.3  to  0.5  gallon  per  square  yard,  after 
which  sufficient  stone  screenings,  running  from  one-half  inch 
to  dust,  are  applied  to  fill  the  surface  voids  and  take  up  any 
excess  of  bitumen.  The  screenings  which  have  been  previously 
swept  from  the  surface  may  be  used  for  this  purpose.  The 
road  is  completed  by  a  final  rolling,  but  should  preferably  not 
be  opened  to  traffic  for  a  few  days  or  until  the  green  bitumen 
has  had  a  chance  to  come  to  a  sort  of  set.  In  this  work  ex- 
cessive rolling  should  be  avoided  before  applying  the  bitumen, 
as  too  free  a  use  of  the  roller  causes  the  stones  to  become 
rounded  and  covered  with  dust,  thus  preventing  proper  inter- 
locking of  the  individual  fragments  with  one  another,  as  well  as 
good  adhesion  of  the  bitumen  to  the  stone  surfaces. 

The  hot  bitumen  may  be  applied  either  by  hand,  directly 
from  portable  tar  kettles  or  by  means  of  sprinklers  as  described 
under  the  surface  treatment  of  roads.  Two  types  of  portable 
kettles  suitable  for  this  work  are  shown  in  Figs.  26  and  29. 

Fig.  26  has  already  been  described.  In  Fig.  29  is  shown  an 
asphaltic  oil  heating  truck.  "The  body,  or  fire  box  of  the 
truck,  as  well  as  the  tank,  is  made  of  the  best  grade  No.  8  sheet 
steel.  The  tank  is  built  separate  from  the  body  or  fire  box 
of  the  truck,  and  in  the  event  of  the  tank  becoming  burned 
or  otherwise  damaged,  it  can  easily  be  removed  from  the  setting 


TAR   AND   CONSTRUCTION    OF   BITUMINOUS    MACADAM     295 


and  be  repaired.  The  furnace  is  made  in  box  form  of  steel 
plates,  the  sides  being  reinforced.  The  truck  is  mounted  on 
four  wheels  of  large  diameter  and  broad  tread. 

"  An  arrangement  of  a  rack  of  light  construction  is  provided  on 
the  top  of  the  kettle  for  carrying  three  barrels  of  material. 
This  rack  is  covered  by  a  galvanized  iron  hood  of  light  con- 
struction for  the  purpose  of  retaining  the  heat  arising  from  the 


FIG.  29.     Asphaltic  Oil  Heating  Truck  (Iroquois  Iron  Works). 

setting  and  utilizing  it  for  heating  the  barrels  of  material 
carried  on  the  rack.  The  hood  is  provided  with  three  handles 
on  either  side,  rendering  it  easily  removed. 

"This  kettle  is  so  designed  that  it  can  be  operated  with 
equally  good  results  by  the  burning  of  oil  or  wood.  For  the 
burning  of  oil  there  is  arranged  on  the  front  of  the  machine  a 
fuel  tank  having  a  capacity  of  thirty  gallons.  Three  oil  burners 
and  the  necessary  piping,  air  compressor,  pressure  gauge,  valves, 
shut-off  cocks,  etc.,  are  all  arranged  as  a  unit,  which  may  be 


2Q6  DUST   PREVENTIVES    AND    ROAD   BINDERS 

easily  detached.  When  wood  is  desired  as  the  fuel,  the  unit  can 
readily  be  removed  and  substituted  with  a  solid  door  furnished 
with  the  truck. 

"For  the  easy  handling  of  barrels  of  material  from  the  ground, 
steel  skids  are  provided,  arranged  to  hook  over  the  end  framing, 
directly  over  the  fuel  tank;  when  not  in  use  they  can  be  hung 
on  hooks,  on  the  side  of  the  fire  box,  provided  for  the  purpose. 

"The  kettle  is  equipped  with  a  3-inch  pipe  and  draw-off 
cock,  arranged  in  a  straight  line,  so  that  should  the  asphaltic  oil 
become  congealed,  the  piping  and  draw-off  can  be  readily 
cleaned  with  a  rod  which  is  provided  for  that  purpose." 

A  very  good  arrangement  for  distributing  the  bitumen  when 
kettles  of  this  sort  are  used  is  to  connect  a  heavy  rubber  hose 
carrying  a  fan  shaped  copper  nozzle  to  the  draw-off.  This 
nozzle  should  be  about  12  inches  in  length  and  fitted  with 
a  slot  one-eighth  inch  wide.  When  applying  the  tar  it  is  worked 
backward  and  forward  across  the  entire  width  of  the  road  and 
only  a  few  inches  from  the  surface,  the  direction  of  the  slot 
being  parallel  to  the  length  of  the  road.  By  this  means  a 
fairly  uniform  distribution  may  be  secured  with  a  little  prac- 
tice, with  slight  chance  of  the  bitumen  cooling  to  any  extent 
before  coming  in  contact  with  the  roadstone.  In  order  to 
avoid  disturbing  the  upper  course  of  stone  while  the  tar  is 
being  applied,  it  is  sometimes  advisable  to  finish  only  one-half 
the  width  at  a  time.  In  the  treatment  of  the  first  half  the 
wearing  course  is  laid  from  one  gutter  to  only  a  little  beyond 
the  center  of  the  road.  The  heating  kettle  is  then  moved 
along  the  foundation  course  and  the  bitumen  applied  to  the 
opposite  side  by  means  of  the  long  hose  and  fan  shaped 
nozzle  before  described.  After  one-half  of  the  width  is  finished 
the  wearing  course  may  be  laid  on  the  other  side  so  as  to  pro- 
duce a  feather  edge  joint  along  the  center,  and  application 
made  in  the  same  manner,  by  moving  the  kettle  along  the 
finished  section.  If  a  mechanical  sprinkler  or  spraying  cart  is 
used,  it  will  be  found  necessary  to  run  it  over  the  unbounded 
wearing  course,  in  which  case  it  will  rut  the  surface  and  if 


TAR   AND    CONSTRUCTION    OF   BITUMINOUS    MACADAM       297 

horse  drawn  will  tear  it  up  badly.  After  the  bitumen  is  ap- 
plied these  inequalities  are  difficult  to  obliterate  and  an  uneven 
surface  is  likely  to  be  produced  if  particular  attention  is  not 
paid  to  raking  the  loose  stone  into  place  and  rolling  carefully. 

The  object  of  the  penetration  method  is  to  produce  a  bitumi- 
nous concrete  wearing  surface  without  depending  upon  labor  or 
machinery  for  mixing.  As  has  been  stated,  an  attempt  is  made 
to  cover  the  upper  two  inches  of  stone.  While  the  whole  sur- 
face may  be  covered  with  comparatively  little  bitumen,  a  uniform 
penetration  for  the  depth  of  two  inches  cannot  be  secured  with 
less  than  one  gallon  of  bitumen  per  square  yard.  This  will 
amount  to  approximately  a  6  per  cent  mixture,  which  is  about 
right  for  bituminous  macadam  construction.  If  lasting  results 
are  to  be  expected,  no  smaller  quantity  should  be  applied.  The 
seal  coat  of  approximately  0.5  gallon  of  bitumen  to  the  square 
yard  is  very  desirable,  as  it  protects  the  underlying  thinner  films 
from  weathering  and  disintegrating.  In  some  cases  attempts 
have  been  made  to  construct  a  macadam  road  according  to 
this  method  with  only  a  little  over  0.5  gallon  of  bitumen  per 
square  yard  all  told.  This  amounts  to  nothing  more  than  a 
surface  treatment  and  the  bitumen  can,  therefore,  only  be 
expected  to  serve  in  the  capacity  of  a  semipermanent  binder. 
Roads  so  constructed  will  usually  require  additional  treatment 
at  the  beginning  of  the  next  season. 

The  main  disadvantages  of  the  penetration  method  of  con- 
struction are  (i)  the  uncertainty  of  obtaining  a  uniform  dis- 
tribution of  bitumen  throughout  the  wearing  surface,  (2)  lack 
of  uniformity  of  the  mineral  aggregate  and  (3)  necessity  of  em- 
ploying a  binder  of  softer  consistency  and  lower  mechanical 
stability  than  is  desirable  for  a  permanent  matrix.  The  first 
objection  is  probably  the  most  serious.  No  matter  how  much 
care  is  taken  in  application,  it  is  impossible  to  be  certain  that  a 
uniform  distribution  has  been  secured.  Small  channels  in  the 
wearing  course  are  likely  to  drain  the  hot  bitumen  away  from 
certain  portions  and  tend  to  concentrate  it  in  others.  A  patch 
of  dust  here  and  there  or  a  few  damp  stones  may  completely 


298  DUST   PREVENTIVES    AND    ROAD   BINDERS 

prevent  absorption  at  these  points.  Moreover,  if  the  surface 
is  a  trifle  too  cold  or  the  bitumen  not  quite  hot  enough,  when  it 
strikes  the  road,  penetration  may  be  almost  completely  cut  off 
by  the  binder  congealing  and  sealing  the  surface.  All  of  this, 
while  not  very  apparent  at  first,  is  apt  to  show  up  as  the  road  is 
subjected  to  traffic.  Soft  wavy  places  may  develop  where  the 
bitumen  has  become  concentrated  and  other  places  may  ravel 
out  where  there  is  a  lack  of  binder.  If  a  thick  coat  of  bitumen  has 
congealed  on  the  surface,  the  road  will  become  soft  and  sticky  in 
warm  weather  and  in  cold  weather  is  likely  to  pick  up  and  peel 
off  under  the  action  of  traffic. 

Lack  of  uniformity  in  the  mineral  aggregate,  except  as  it 
affects  the  distribution  of  the  binder,  probably  produces  no  more 
serious  results  than  in  ordinary  macadam  construction.  Uni- 
formity is,  however,  a  most  desirable  feature  and  can  be  much 
better  controlled  in  the  mixing  method  which  will  be  described 
later.  While  it  is  necessary  to  employ  a  binder  of  sufficiently 
soft  consistency  not  to  congeal  immediately  upon  coming  in 
contact  with  the  roadstone  under  normal  conditions,  and  while 
such  materials  are  perhaps  necessarily  deficient  in  binding 
value  for  construction  work,  it  is  possible  by  proper  selection  to 
obtain  one  which  will  have  the  property  of  attaining  the  desired 
consistency  after  application.  Cut-back  oil  or  tar  products 
which  hold  a  certain  amount  of  readily  volatile  constituents  are 
best  suited  for  this  kind  of  work.  As  a  rule  they  should  have 
sufficient  original  consistency  to  barely  flow  when  cold,  or  other- 
wise the  road  surface  will  be  soft  and  wavy  for  some  time  after 
application. 

In  spite  of  the  objections  which  have  been  advanced  against 
the  penetration  method,  it  has  the  advantage  of  being  cheap,  and 
under  favorable  conditions  of  producing  a  very  satisfactory  road 
for  traffic  which  is  not  excessive.  If  the  binder  is  applied  in 
warm  dry  weather  during  the  heat  of  the  day,  it  is  often  possible, 
although  never  absolutely  certain,  to  obtain  a  surprisingly  uni- 
form distribution,  and  in  a  number  of  instances  which  have  come 
under  the  author's  notice,  upon  digging  into  the  road  surface  at 


TAR  AND    CONSTRUCTION   OF   BITUMINOUS    MACADAM     299 

almost  any  point,  the  stone  fragments  have  been  found  to  be 
exceedingly  well  coated.  Work  of  this  nature  should  cost  but  a 
few  cents  per  square  yard  plus  the  price  of  one  and  one-half  to 
two  gallons  of  binder  over  that  of  ordinary  macadam,  as  the 
labor  of  applying  the  binder  is  small,  providing  that  suitable 
heating  and  spreading  devices  are  employed,  and  the  very  con- 
siderable cost  of  watering  made  necessary  in  regular  macadam 
construction  is  entirely  eliminated.  In  many  cases,  however, 
the  cost  of  such  work  has  been  excessive  owing  to  makeshift 
apparatus  employed,  which  requires  much  labor  to  operate 
and  many  costly  delays  through  breakage  and  inefficiency. 
Now  that  suitable  heating  and  spreading  devices  can  be  pur- 
chased in  this  country,  it  will  prove  extremely  poor  economy  to 
attempt  to  work  with  inferior  appliances,  not  only  because  of 
greater  labor  costs,  but  also  unsatisfactory  results  which  are 
more  than  likely  to  follow  the  use  of  crude  apparatus. 

Before  leaving  the  penetration  method,  mention  should  be 
made  of  the  so-called  bituminous  sand  filled  macadam  which  has 
been  advocated  by  some.  This  type  of  road  is  quite  similar  to 
that  already  described,  but  certain  modifications  are  made 
which  allow  the  use  of  a  more  fluid  bituminous  binder.  Upon 
the  foundation  course  prepared  in  the  usual  manner  a  four  inch, 
layer  of  crushed  stone  ranging  from  one-half  to  one  and  one- 
quarter  inch  in  size  is  laid  and  thoroughly  rolled.  A  filler  of 
sharp  clean  sand  or  stone  chips  free  from  dust  and  not  larger 
than  one-quarter  inch  is  then  applied  and  rolled  into  the  road.  A 
number  of  light  applications  should  be  made  until  the  road  will 
take  up  no  more.  All  excess  is  then  swept  from  the  surface 
and  the  heated  bitumen  applied  at  the  rate  of  approximately 
one  gallon  per  square  yard.  As  the  voids  in  the  wearing 
course  have  been  fairly  well  filled  by  the  sand  or  stone  chips, 
it  is  necessary  to  employ  a  binder  which  is  quite  fluid  at  ordi- 
nary temperatures  in  order  that  a  good  penetration  may  be 
secured.  This  is  also  allowable  as  the  mineral  aggregate  has 
greater  mechanical  stability  than  in  the  regular  penetration 
method. 


300  DUST   PREVENTIVES   AND    ROAD    BINDERS 

After  the  binder  has  been  absorbed  by  the  road  surface,  which 
may  take  from  three  to  seven  hours,  a  light  coat  of  clean  one- 
half  inch  stone  chips  is  applied  and  rolled  into  the  surface 
voids.  A  paint  coat  of  hot  bitumen  at  the  rate  of  approximately 
one-half  gallon  per  square  yard  is  next  applied  and  the  road 
finished  by  rolling  in  sufficient  screenings  to  take  up  all  excess 
of  bitumen.  Roads, so  constructed  are  fairly  well  adapted  to 
withstand  moderately  heavy  mixed  traffic. 

Resurfacing,  Penetration  Method.  —  The  penetration  method 
may  be  followed  when  resurfacing  old  macadam  roads  as  well 
as  when  constructing  new  roads.  In  such  cases  the  old  surface 
should  be  spiked  up  or  scarified  and  brought  to  even  crown 
and  grade  by  the  addition  of  fresh  stone  where  necessary.  It 
is  then  rolled  until  firm,  after  which  it  is  made  to  serve  as  a 
foundation  for  the  wearing  course,  which  is  laid  and  treated  with 
bitumen  in  exactly  the  same  manner  as  described  for  construc- 
tion work.  If  it  is  desired  to  apply  less  than  two  inches  of  fresh 
stone,  the  foundation  should  be  well  harrowed  before  rolling  in 
order  to  work  the  very  fine  material  of  the  old  surface  further 
into  the  body  of  the  road  and  thus  allow  a  deeper  penetration 
of  the  bitumen. 

Bituminous  Macadam  Construction,  Mixing  Method.  —  The 
construction  of  bituminous  macadam  according  to  the  mixing 
method  is  identical  with  the  penetration  method  up  to  the 
completion  of  the  foundation  course.  The  wearing  course, 
which  is  usually  laid  to  a  finished  depth  of  two  or  two  and 
one-half  inches,  is  composed  of  a  more  or  less  carefully  graded 
mineral  aggregate  which  has  been  previously  mixed  and  coated 
with  a  hot  bituminous  binder.  Sometimes  the  aggregate  itself 
is  heated  before  mixing  and  sometimes  used  cold.  In  the 
former  case  a  binder  of  high  original  consistency  may  be 
employed,  while  in  the  latter  it  should  have  about  the  same 
properties  as  one  which  is  to  be  used  according  to  the  pene- 
tration method.  For  a  number  of  reasons  the  heated  aggregate 
is  to  be  preferred.  The  mixture  may  be  made  either  by  manual 
labor  or  by  machinery,  as  described  below. 


TAR   AND    CONSTRUCTION    OF   BITUMINOUS    MACADAM     301 

After  the  bitumen  coated  stone  has  been  laid  to  the  desired 
depth  it  is  rolled  either  with  or  without  the  addition  of  one-half 
inch  stone  chips  free  from  dust.  Where  the  latter  can  be  done 
without  the  stone  sticking  to  the  roller  wheels  a  very  satisfactory 
surface  may  be  secured  by  the  application  of  a  light  coating  of 
bitumen  covered  sand  or  stone  chips  which  is  rolled  into  the  sur- 
face voids  and  dusted  over  with  stone  dust  or  cement.  In  the 
former  case  all  surplus  of  screenings  should  be  broomed  off  and 
a  flush  or  paint  coat  of  bitumen  applied  at  the  rate  of  from  0.3 
to  0.5  gallon  per  square  yard,  after  which  screenings  are  again 
applied  and  rolled  down  in  sufficient  quantity  to  take  up  the 
excess  of  bitumen. 

Theoretically,  in  order  to  acquire  the  maximum  degree  of 
stability  the  mineral  aggregate  should  be  so  graded  that  if  a 
given  space  is  filled  with  the  largest  size  fragments,  the  other 
sizes  will  be  so  proportioned  that  the  next  smaller  will  occupy 
only  the  voids  between  the  first  size,  the  next  smaller  the  re- 
maining voids  and  so  on  down  to  an  impalpable  powder.  While 
particular  attention  is  paid  to  the  grading  of  a  sheet  asphalt 
topping  and  also  to  the  wearing  course  of  the  type  of  pavement 
known  as  bitulithic,  such  refinement  is  far  too  expensive  for 
ordinary  country  highway  construction  and  for  the  most  part 
unnecessary.  Bitulithic,  because  of  its  high  cost  at  the  present 
time,  may  be  classed  as  a  city  pavement.  Where  less  refined 
methods  of  grading  and  mixing  the  aggregate  are  followed 
good  results  may  be  obtained  in  the  construction  of  country 
and  suburban  highways  at  a  very  much  lower  cost.  Other  things 
being  equal,  dense  surface  mixtures  containing  a  minimum  per- 
centage of  voids  are  to  be  preferred  to  those  having  a  higher  per- 
centage of  voids.  Maximum  inherent  stability  or  capacity  for 
resistance  to  displacement  of  the  individual  constituents  of  an 
aggregate  is  not  only  dependent  upon  the  proportion  and  arrange- 
ment of  these  constituents  but  also  upon  the  size  of  the  largest 
fragments.  This  fact  has  been  recognized  for  a  long  time  and 
has  undoubtedly  governed  the  construction  not  only  of  bitumi- 
nous macadam  roads,  but  of  ordinary  macadam  as  well.  It 


302  DUST   PREVENTIVES   AND    ROAD    BINDERS 

remained,  however,  for  Frederick  J.  Warren  to  state  in  a  very 
broad  way  the  size  and  proportions  of  the  constituents  of  a 
mineral  aggregate  which  should  possess  inherent  stability. 
In  1901  he  was  granted  a  patent  *  covering  a  combination  of 
graded  broken  stone  and  dust  of  different  sizes,  so  proportioned 
that  the  whole  should  have  a  very  low  percentage  of  voids,  and 
mixed  with  about  6  per  cent  of  a  bituminous  cement.  In  this 
patent  the  sizes  of  stone  are  stated  in  the  following  proportions : 

Broken  stone  from  3"  to  \" 70  parts 

Broken  stone  from  \"  to  fa" 20     " 

Broken  stone  from  fa"  to  fa" 20     " 

Broken  stone  from  fa"  to  fa" 4     " 

Dust  less  than  fa"  to  2-  fay" 3     " 

Dust  less  than  ^faj-" I     " 

In  1903  Warren  was  granted  another  patent  f  covering  the  use 
of  a  mineral  aggregate,  in  combination  with  a  bituminous  binder, 
proportioned  as  follows: 

From  3"  to  J" 50  to  80% 

From  J"  to  impalpable  powder 10  to  49% 

Impalpable  powder i  to    3% 

His  idea  was  that  mineral  aggregate  so  proportioned  would 
possess  sufficient  inherent  stability  to  make  it  possible  to 
employ  a  very  much  more  fluid  binder  than  in  the  case  of  sheet 
asphalt  topping,  where  all  of  the  constituents  are  of  small  size. 
While  the  larger  size  fragments  are  desirable  on  this  account 
too  large  a  maximum  is  apt  to  produce  a  surface  mixture  which 
will  wear  unevenly  under  traffic.  It  is  probable  that  the  use 
of  stone  which  will  pass  a  two  inch  ring  will  in  practice  prove 
the  best  maximum  to  adopt,  except  in  the  case  of  soft  rock. 
The  old  coal  tar  pavement  mentioned  at  the  beginning  of  this 
chapter  may  be  considered  as  a  good  example  of  this  type. 

In  country  road  work  it  is  for  the  most  part  impracticable  to 
carefully  grade  and  proportion  the  various  sizes  of  stone.  For 
reasons  of  economy  it  is  often  necessary  to  make  use  of  the 

*  U.  S.  Patent,  675,  430. 
f  U.  S.  Patent,  727,  505. 


TAR   AND    CONSTRUCTION    OF   BITUMINOUS    MACADAM     303 

entire  crusher  run  of  material,  and  the  crusher  run  is  at  best 
separated  into  three  or  four  sizes.  For  ordinary  purposes  a 
roughly  graded  aggregate  composed  of  a  mixture  of  two  or 
three  of  these  sizes  can  be  made  to  give  satisfactory  results. 
Thus,  for  a  rock  that  produces  comparatively  little  dust  upon 
being  crushed,  a  mixture  of  twenty-seven  parts  by  weight  of 
stone  one  and  one-half  to  three-fourths  inches  in  size  to  ten  parts 
of  screenings  three-fourths  inch  to  dust  has  been  found  to  pro- 
duce a  very  satisfactory  mixture.  Where  the  dust  is  excessive, 
screenings  free  from  dust  may  be  used  and  a  small  amount  of 
dust  afterwards  added. 

As  in  cement  concrete  work  it  will  prove  an  excellent  plan  to 
make  up  trial  batches  before  work  is  commenced  in  order  to  deter- 
mine the  densest  practicable  mixture.  This  can  be  done  by  mak- 
ing two  cubical  boxes,  one  to  hold  an  even  cubic  foot  of  material 
and  the  other  with  a  capacity  of  six  cubic  feet.  A  total  of  six 
cubic  feet  of  material  may  be  measured  out  in  any  desired  pro- 
portion by  means  of  the  smaller  box,  and  thoroughly  mixed. 
The  mixture  is  then  placed  in  the  larger  box,  struck  level  and 
its  depth  noted.  That  mixture  showing  the  lowest  depth  will 
be  the  densest.  It  is  probable,  however,  that  in  no  case  should 
the  amount  of  crushed  stone  larger  than  one-half  inch  screen- 
ings be  less  than  the  screenings  and  dust  combined. 

Resurfacing,  Mixing  Method.  —  The  mixing  method  may  be 
employed  in  resurfacing  old  roads  as  well  as  in  constructing 
new  ones.  For  this  work  the  old  road  should  be  spiked  up 
and  recrowned  in  the  same  manner  as  described  under  resur- 
facing according  to  the  penetration  method.  The  presence  of 
an  excessive  amount  of  fine  material  on  the  surface  of  the  foun- 
dation course  thus  prepared  should  be  particularly  guarded 
against  in  order  that  the  wearing  course  shall  not  be  prevented 
from  keying  into  the  stone  below.  The  wearing  course  may  then 
be  prepared,  laid  and  finished  off  in  exactly  the  same  manner 
as  for  construction  work. 

Hand  Mixing.  —  While  mixing  machinery  is  unquestionably 
to  be  preferred  in  carrying  on  extensive  work,  it  may  some- 


304  DUST   PREVENTIVES   AND    ROAD   BINDERS 

times  be  desired  to  construct  short  sections  of  road  where  the 
use  of  such  machinery  will  not  prove  economical.  In  a  recent 
article  *  the  author  has  described  a  method  of  hand  mixing 
bituminous  concrete  for  road  work,  which  he  has  himself  used, 
and  this  description  is  here  included  for  the  use  of  those  who 
desire  to  do  similar  work.  The  method  was  employed  by  the 
Office  of  Public  Roads  in  cooperation  with  Mr.  Charles  W. 
Ross,  Street  Commissioner  of  Newton,  Massachusetts,  during 
the  summer  of  1908. 

It  may  first  be  stated  that  if  such  work  is  to  be  conducted 
upon  an  economical  basis,  the  most  essential  factor  to  be  con- 
sidered is  the  proper  arrangement  and  control  of  labor.  Under 
ordinary  conditions  the  construction  of  a  bituminous  macadam 
road  represents  the  combined  labor  of  three  working  units, 
which  may  be  called  the  mixing  force,  the  teaming  force  and 
the  construction  force.  As  it  is  of  course  necessary  that  some 
material  be  mixed  before  the  construction  force  can  begin  to  lay 
the  bitumen  coated  material,  and  as  in  many  instances  it  is  prefer- 
able to  carry  on  the  mixing  operation  near  the  source  of  stone 
supply,  it  is  evident  that  these  three  units  should  begin  work 
at  different  hours,  in  order  that  they  may  all  be  kept  constantly 
employed.  In  other  words,  the  mixing  force  should  begin  work 
at  an  earlier  hour  than  the  teaming  force  and,  depending  upon 
the  length  of  haul,  the  teaming  force  should  begin  work  at  an 
earlier  hour  than  the  construction  force. 

With  this  understanding  we  may  eliminate  the  two  latter  and 
consider  only  the  mixing  force.  In  the  work  at  Newton  the 
following  method  of  procedure  was  evolved  and  proved  satis- 
factory in  regard  to  both  efficiency  and  economy: 

The  mixing  plant  was  located  quite  close  to  the  crushing 
plant,  as  shown  in  Fig.  30.  The  working  force  consisted  of 

1  foreman,  1 5  laborers,  and  i  single  team,  and  the  apparatus  of 

2  two-barrel  heating  kettles,  3  stone  heaters,  2   stone  gauges, 
i  mixing  platform,  12  long  handled  shovels,  2  iron  rakes,  and  i 

*  "  Hand  Mixing  for  Bituminous  Macadam  Construction,"  Good  Roads  Maga- 
zine t  September,  1909. 


TAR   AND   CONSTRUCTION   OF  BITUMINOUS   MACADAM       30$ 


306  DUST  PREVENTIVES   AND   ROAD   BINDERS 

long  handled  one-gallon  bitumen  ladle.  Wood  was  employed 
for  fuel.  With  this  equipment  it  was  found  possible  to  prepare 
under  favorable  conditions  37  cubic  yards  of  a  dense,  evenly 
coated  mineral  aggregate  per  day  of  eight  working  hours.  The 
detailed  cost  data  is  given  in  the  table  below. 

The  mixing  platform  measured  approximately  20  feet  in 
width  by  30  feet  in  length  and  was  made  by  laying  2-inch 
planks  side  by  side  and  as  close  together  as  possible  upon  a 
level  piece  of  ground.  The  stone  heaters  were  semicylindrical 
in  shape  and  measured  8  feet  in  length,  4  feet  6  inches  in  width, 
and  1 8  inches  in  height.  They  were  constructed  of  five-six- 
teenth-inch boiler  iron  with  three  inside  lateral  braces  and 
closed  at  one  end.  At  the  closed  end  of  each  heater  was  fitted 
a  6-foot  smoke  stack  1 2  inches  in  diameter.  These  three  heaters 
were  arranged  about  the  platform  as  shown  in  the  illustration. 
The  stone  gauges  were  of  the  ordinary  bottomless  box  type 
fitted  with  handles.  The  one  for  gauging  the  small  stone,  which 
ran  from  three-fourths  inch  to  dust  just  as  it  came  from  the 
crusher,  held  when  level  full  about  350  pounds  of  stone.  The 
other,  for  gauging  the  larger  stone,  running  from  one  and  one- 
half  inch  to  three-fourths  inch,  held  about  960  pounds  of  stone. 
One  gauge  of  each  size  combined  was  found  to  be  a  very  satis- 
factory quantity  for  four  men  to  mix  at  one  time.  The  two 
side  heaters  were  employed  for  heating  the  large  stone,  the 
end  heater  for  the  small  stone. 

It  was  found  most  convenient  to  mix  two  batches  of  stone  at 
the  same  time,  the  arrangement  of  labor  and  modus  operandi 
being  as  follows.  The  single  team  kept  the  stone  pile  beside 
each  heater  constantly  replenished  and  at  intervals  assisted  in 
hauling  the  bituminous  mixture  to  the  road.  One  laborer  was 
detailed  to  attend  to  the  heating  kettles  and  began  work  30 
minutes  earlier  than  the  rest  of  the  force,  in  order  to  have  a 
supply  of  hot  bitumen  ready  at  the  start.  As  required,  two 
men  from  the  rest  of  the  force  assisted  in  rolling  the  barrels 
of  bitumen  upon  barrel  platforms,  from  which  they  could  be 
emptied  into  the  kettle  not  in  use.  In  this  way  all  delay  in 


TAR  AND   CONSTRUCTION   OF  BITUMINOUS   MACADAM    307 

waiting  for  the  bitumen  to  be  heated  was  avoided.  The  fore- 
man directed  the  work  of  mixing  and  measuring  out  the  hot 
bitumen.  At  each  heater  two  men  were  employed  in  heating 
the  stone  which  they  took  from  the  pile  nearby.  With  a  bitu- 
men of  such  consistency  that  at  ordinary  summer  tempera- 
ture it  would  drain  slowly  from  the  bung  of  the  barrel,  it  was 
found  that  with  a  good  fire  beneath  the  heater  the  stone  would 
become  sufficiently  warm  for  mixing  in  a  very  short  time.  The 
operation  of  loading  and  unloading  the  heaters  was,  therefore, 
almost  continuous. 

Four  laborers  were  employed  in  mixing  each  batch  of  stone. 
The  small  gauge  was  first  placed  near  the  rear  of  the  platform 
and  at  an  equal  distance  from  the  rear  heater  and  one  of  the  side 
heaters,  and  was  filled  with  the  hot  fine  stone  from  the  rear 
heater.  It  was  then  removed  to  a  similar  position  on  the  other 
side  of  the  platform  for  measuring  the  second  batch.  The  pile 
of  stone  so  deposited  was  flattened  out  so  that  the  large  gauge 
could  be  placed  upon  it,  and  this  gauge  was  filled  with  large  stone 
from  the  nearest  side  heater.  It  was  then  used  iri  a  similar  man- 
ner for  the  second  batch  of  stone,  which  was  prepared  in  exactly 
the  same  way.  At  this  point  the  foreman  spread  four  gallons  of 
hot  bitumen  upon  the  prepared  pile  of  stone,  and  three  laborers 
immediately  began  to  turn  it  over  from  the  bottom  with  shovels, 
working  the  pile  toward  the  front  of  the  platform.  A  fourth 
laborer  raked  the  turned  pile  as  it  was  being  formed.  After 
the  first  turning  two  more  gallons  of  hot  bitumen  were  applied 
by  the  foreman  and  the  pile  again  turned  and  raked  in  the  same 
manner  as  before,  thus  bringing  the  mixture  to  the  front  of  the 
platform,  where  it  was  ready  to  be  loaded  upon  the  wagon  to  be 
carried  to  the  road.  This  operation  was  at  the  same  time  being 
repeated  by  another  set  of  men  on  the  other  side  of  the  platform. 

When  prepared  in  the  manner  described,  two  turnings  were 
sufficient  to  secure  a  uniform  mixture  in  which  each  fragment  of 
stone  was  thoroughly  coated  with  bitumen.  It  was  found  that  if 
the  fine  material  was  not  placed  at  the  bottom  of  the  pile  before 
mixing,  from  four  to  six  turnings  were  required  in  order  to 


308 


DUST   PREVENTIVES   AND    ROAD    BINDERS 


secure  a  uniform  mixture.  This  was  due  to  the  fact  that  if  the 
fine  stone  was  coated  first,  so  much  bitumen  was  absorbed  that 
it  was  a  difficult  matter  to  get  the  larger  particles  covered. 
In  order  to  avoid  loss  of  time  at  the  construction  end  of  the  work, 
one  man  from  each  mixing  gang  assisted  the  teamsters  in  loading 
the  mixture  upon  the  wagons  as  occasion  arose. 

It  was  found  that  this  mixture  was  so  dense  that  it  compacted 
but  little  under  the  roller,  so  that  where  a  two  inch  course  of 
bitumen-covered  stone  was  desired  upon  the  ordinary  foundation 
course,  i  cubic  yard  would  cover  practically  eighteen  square 
yards  of  road.  Work  so  conducted  showed  the  following  cost  for 
mixing.  Interest  on  capital  invested  for  and  loss  for  deprecia- 
tion of  apparatus  are  included.  Allowance  for  delays  because  of 
rainy  weather  should  also  be  made,  but  as  this  is  an  uncertain 
factor  it  is  not  considered  in  the  table  of  cost. 

COST    DATA    OF    HAND    MIXING. 


Per  Day. 

Per  Sq. 
Yard. 

i  foreman  at  $2  ^o                 '                 .... 

$2     CO 

Cents. 
?8 

i  c  laborers  at  $2  oo         .                

•3Q     OO 

4r  T 

i  single  team  at  $3  ^o                   

3CQ 

r  -2 

^  cord  of  wood  at  $6.00  per  cord  
Setting  up  and  removing  plant  (basis  of  30  days)  

2.00 
4O 

•3° 
06 

Interest  on  capital  invested  at  6  per  cent  per  annum  ) 
Depreciation  of  apparatus  at  12  per  cent  per  annum  J 

•13 

.02 

Total           

$^8     C7 

r    80 

Bitumen  in  mixture 

Per  Square 
Yard, 
o  8  gal 

Bitumen  painted  on  road  surface       

r    oral 

Total            

I    3  £fal 

When  the  mixing  method  is  employed  the  cost  of  watering 
should  be  deducted  in  order  to  ascertain  the  excess  cost  over 
the  ordinary  form  of  macadam  construction.  Best  practise,  on 
the  other  hand,  requires  that  a  coat  of  hot  bitumen  be  painted 


TAR    AND    CONSTRUCTION    OF   BITUMINOUS    MACADAM     309 

upon  the  rolled  course  of  bitumen  covered  stone,  and  the  labor 
thus  entailed  has  been  allowed  to  offset  the  cost  of  watering  in 
obtaining  the  final  excess  cost.  As  the  cost  of  various  bitumin- 
ous binders  also  differs  greatly,  only  the  approximate  quantity 
required  is  given  in  the  above  table.  From  these  figures,  how- 
ever, it  is  seen  that  under  favorable  conditions  a  macadam  road 
constructed  with  a  two  inch  top  course  of  bitumen-covered  stone 
should  not  cost  over  six  cents  per  square  yard  plus  the  cost  of 
1.3  gallon  of  bitumen  delivered,  over  and  above  the  cost  of  an 
ordinary  macadam  road  of  the  same  depth. 

A  better  type  of  heating  kettle,  for  such  work,  than  those 
described  above  is  shown  in  Fig.  29. 

Mechanical  Mixing.  —  There  are  a  number  of  excellent 
portable  mixers  manufactured  in  this  country  for  preparing 
bituminous  concrete,  and  their  use  is  certainly  to  be  advocated 
where  long  stretches  of  bituminous  macadam  roads  are  to  be 
constructed.  Some  of  these  mixers  are  very  complete,  being 
equipped  to  heat  both  stone  and  bitumen  and  automatically 
proportion  and  mix  the  concrete.  Ordinary  cement  concrete 
mixers  are  hardly  suited  for  preparing  bituminous  concrete, 
although  they  are  sometimes  employed  for  this  purpose.  An 
asphalt  mixer  of  the  type  shown  in  Fig.  31  is  to  be  greatly 
preferred.  This  mixer  is  equipped  with  a  double  set  of  revolving 
blades  inclined  to  the  right  and  left,  which  arrangement  has 
proved  the  most  successful  for  turning  out  a  well  coated  uniform 
concrete  at  a  rapid  rate.  These  blades  are  so  set  upon  the  shafts 
that  the  mixture  is  continually  tossed  upward  and  at  the  same 
time  worked  toward  the  center.  The  lever  operates  to  open  a 
slide  in  the  bottom  of  the  mixer  through  which  the  concrete  is 
discharged. 

In  Fig.  32  is  shown  a  modern  auto-portable  paving  plant  well 
equipped  to  turn  out  bituminous  concrete  for  road  work.  A 
twenty  horsepower  steam  boiler  supplies  power  to  both  move  the 
machine  and  operate  the  entire  plant.  This  plant  consists  of  a 
drying  cylinder;  a  furnace  to  heat  the  cylinder  and  melt  the 
bituminous  cement;  a  heating  tank  located  above  the  furnace  and 


3IO  DUST  PREVENTIVES   AND   ROAD   BINDERS 

capable  of  holding  300  gallons  of  bitumen;  an  automatic  measur- 
ing device  for  proportioning  both  the  bitumen  and  aggregate;  a 
mixer  under  which  is  located  a  small  furnace  for  maintaining  a 
uniform  temperature  during  the  mixing  process;  and  a  dust  col- 
lector. The  drying  cylinder  is  three  feet  in  diameter  by  eighteen 
feet  in  length,  and  is  so  constructed  that  the  mineral  aggre- 
gate is  moved  steadily  forward  toward  the  dumping  end,  mean- 
while being  subjected  to  an  even  degree  of  heat  which  thoroughly 


FIG.  31.    Asphalt  Concrete  Mixer  (Iroquois  Iron  Works). 

dries  and  heats  it  so  that  it  can  be  readily  mixed  with  the  hot 
bitumen.  The  automatic  measuring  device  regulates  the  amount 
of  aggregate  that  goes  into  the  mixer  and  is  divided  into  two 
compartments  so  that  one  can  be  filling  while  the  other  dis- 
charges. This  device  is  connected  with  measuring  pots  located 
on  the  side  of  the  tank  containing  the  bitumen  and  whenever 
the  mineral  aggregate  is  discharged  into  the  mixer,  one  of  the 


UNIVERSITY 

OF 


TAR   AND   CONSTRUCTION   OF   BITUMINOUS   MACADAM 


312  DUST   PREVENTIVES   AND    ROAD   BINDERS 

measuring  pots  automatically  opens  and  discharges  its  contents 
into  the  mixer  at  the  same  time.  The  plant  is  self-propelling 
and  is  arranged  so  that  each  part  may  be  operated  independently. 
Its  weight  is  approximately  nine  tons.  It  measures  twenty-nine 
feet  in  length,  ten  feet  in  width  and  ten  feet  in  height.  Its 
capacity  is  from  forty-five  to  fifty-five  cubic  yards  per  day,  being 
equivalent  to  the  work  of  about  twenty  men.  This  plant  can 
be  operated  directly  on  the  road  and  the  hot  concrete  laid  as 
soon  as  it  leaves  the  mixer. 

In  cases  where  an  asphaltic  cement  has  to  be  handled  upon  the 
road  it  will  often  be  found  convenient  and  expeditious  to  make 


FIG.  33.    Asphalt  Cutter  (Standard  Asphalt  and  Rubber  Co.). 

use  of  an  asphalt  cutter,  such  as  shown  in  Fig.  33,  for  cutting  the 
cement  into  chunks  before  placing  it  in  the  heater.  The  prin- 
ciple of  this  machine  is  made  apparent  in  the  figure  and  requires 
no  description  other  than  to  state  that  the  asphalt  is  cut  by 
means  of  a  wire. 

In  some  instances  the  road  engineer  may  desire  to  prepare  a 


TAR   AND    CONSTRUCTION   OF  BITUMINOUS   MACADAM     313 


FIG.  34.     Portable  Asphalt-Oil  Mixing  Plant. 

bituminous  binder  which  will  possess  certain  properties  not 
obtainable  in  any  trade  products.  To  meet  this  need  portable 
asphalt-oil  mixing  plants  have  been  devised  for  the  purpose  of 
preparing  any  desired  mixture  of  solid  bitumen  and  flux.  Such 
a  machine,  designed  by  Mr.  J.  C.  Travilla,  Street  Commissioner 
of  St.  Louis,  is  shown  in  Fig.  34. 

"The  plant  consists  of  a  melting  and  agitation  kettle,  air 


314  DUST   PREVENTIVES    AND    ROAD    BINDERS 

pressure  for  furnishing  compressed  air  for  agitating  the  oil 
asphalt  compound  and  for  forcing  it  from  the  melting  kettle  to 
a  distributing  wagon,  a  steam  pump  as  an  auxiliary  for  pumping 
heavy  oil  from  the  tank  car  to  the  melting  kettle  and  a  steam 
boiler  for  the  operation  of  the  air  pressure  and  steam  pumps. 
The  kettle  has  a  capacity  of  1350  gallons,  is  divided  transversely 
into  two  equal  parts,  one  compartment  being  intended  for 
melting  and  mixing  the  oil-asphalt  and  the  other  for  agitating 
the  oil-asphalt  by  means  of  air  blown  into  the  contents  of  the 
kettle  under  low  pressure. "  This  plant  is  not  only  useful  for 
preparing  heavy  products  for  construction  work,  but  also  for 
reinforcing  the  lighter  road  oils  with  asphalt  to  any  desired 
consistency  and  binding  value. 

Bituminous  Macadam,  Gladwell  Method.  —  In  1906  a  method 
of  resurfacing  and  constructing  macadam  roads  with  the  use  of  a 
matrix  of  tar  and  sand  or  stone  chips  as  a  binder  was  developed 
in  England  by  Gladwell  and  Manning.  This  method  has  never 
been  adopted  to  any  extent  in  the  United  States,  although  it 
has  found  favor  in  England.  It  may  be  briefly  described  as 
follows. 

The  foundation  course  is  first  prepared  as  in  ordinary  mac- 
adam work,  but  its  surface  should  be  clean  and  free  from  fine 
material.  Upon  the  foundation  is  then  placed  a  layer  of  the 
prepared  matrix,  to  the  depth  of  approximately  i  inch,  called 
the  sub-binder.  This  matrix  should  be  spread  lightly  and 
evenly  and  on  no  account  should  be  consolidated  before  the 
wearing  course  of  stone  is  applied.  The  wearing  course  should 
consist  of  stone  crushed  and  screened  to  the  uniform  size  of 
two  to  two  and  one-fourth  inches,  placed  on  top  of  the  ma- 
trix to  a  depth  of  what  the  inventors  call  a  two  stone  coat. 
The  stone  should  be  spread  from  the  sub-binder  already  laid, 
and  should  be  handled  with  stone  forks  so  as  to  leave  the 
smaller  fragments  and  the  dust  behind  as  waste.  This  course 
is  brought  to  within  6  inches  of  the  forward  end  of  the  sub- 
binder,  after  which  another  strip  of  sub-binder  can  be  laid  for 
about  3  feet  ahead  and  followed  with  the  application  of  coarse 


TAR   AND    CONSTRUCTION    OF  BITUMINOUS    MACADAM    315 

stone,  always  leaving  at  least  6  inches  length  of  the  binder  project- 
ing, and  so  on.  By  this  means  the  working  force  will  be  enabled 
to  lay  both  sub-binder  and  wearing  course  without  trampling  on 
either.  As  soon  as  a  section  25  to  30  feet  in  length  has  been  laid 
in  this  manner,  it  is  rolled  with  a  fairly  light  roller,  the  object 
being  to  press  the  coarse  aggregate  into  the  sub-binder  and 
at  the  same  time  entice  the  binder  upward  into  the  voids  of 
the  aggregate.  The  roller  should  be  run  at  low  speed  and  when 
the  sub-binder  appears  in  places  at  the  top,  a  light  application 
of  fresh  matrix  is  salted  over  the  road  in  sufficient  quantity  to 
fill  the  surface  voids  and  the  rolling  continued  until  the  road  is 
solid.  A  seal  coat  of  hot  bitumen  is  then  applied  and  the  sur- 
face sanded  and  rolled. 

This  method  may  be  considered  as  a  combination  of  the 
penetration  and  the  mixing  methods  and  is  open  to  the  criticism 
urged  against  the  former.  That  is,  uniformity  in  the  resulting 
road  is  never  assured.  The  method  aims  to  produce  a  wearing 
course  of  fairly  large  sized  stones  which  are  bound  together 
and  the  voids  between  which  are  filled  with  the  bituminous 
matrix.  This  condition  of  affairs  is  never  a  certainty  as  it  is  a 
difficult  matter  to  work  the  sub-binder  uniformly  throughout 
the  course.  A  fluid  refined  tar  has  been  almost  exclusively 
used  in  such  work.  About  15  gallons  of  the  tar  are  mixed  with 
one  cubic  yard  of  sand  or  stone  chips  to  form  the  matrix.  Re- 
pairs may  be  made  by  cutting  out  worn  places  to  expose  clean 
surfaces  and  refilling  with  fresh  material  in  the  same  manner  as 
though  constructing  a  new  road. 

Characteristics  of  Bituminous  Macadam.  —  The  appearance 
of  a  well-constructed  bituminous  macadam  after  being  sub- 
jected to  traffic  for  a  short  time  should  be  that  of  a  mosaic 
surface  in  which  the  larger  stones  predominate.  These  large 
stones  take  up  most  of  the  wear  and  are  held  in  place  by  the 
filling  of  smaller  bitumen  covered  fragments.  The  road  should 
be  firm,  resilient  and  waterproof.  The  surface  should  be  even 
but  not  so  smooth  as  to  be  slippery,  the  coarse  grained  aggre- 
gate offering  sufficient  toe  hold  for  horses  even  on  compara- 


DUST   PREVENTIVES   AND    ROAD   BINDERS 

tively  steep  grades.  The  surface  is  dustless  in  the  same  sense 
that  an  ordinary  asphalt  street  is  dustless.  Resistance  to  trac- 
tion is  less  than  that  of  an  ordinary  macadam  unless  too 
much  bitumen  has  been  applied.  While  the  binder  is  not 
supposed  to  bear  any  great  amount  of  external  wear  it  exerts  a 
cushioning  effect  between  the  individual  stones  and  reduces 
internal  wear  by  preventing  them  from  grinding  one  against 
the  other,  under  the  action  of  traffic.  A  few  days  after  being 
laid  all  odor  of  an  objectionable  nature  will  have  disappeared. 
Tar  in  particular,  however,  retains  its  hygienic  and  germicidal 


FIG.  35.     Method  of  Patching  Bituminous  Macadam  Surfaces. 

properties  for  some  time  after  application.  To  determine  this 
point  an  investigation  of  the  relative  number  of  living  germs 
existing  in  the  atmosphere  just  above  a  tarred  and  an  untarred 
road  in  the  same  neighborhood  was  made  in  France  by  Chris- 
tiani  and  Michelis,  who  found  less  than  one-half  the  number  in 
the  former  case  as  the  latter,  both  in  damp  and  dry  weather. 
The  chief  recommendation  of  the  bituminous  macadam,  how- 
ever, is  its  ability  to  successfully  withstand  the  modern  com- 
bined automobile  and  horse  drawn  traffic. 


TAR   AND    CONSTRUCTION    OF   BITUMINOUS    MACADAM 

Probably  the  most  critical  period  in  the  life  of  a  bituminous 
macadam  is  the  first  two  or  three  months  after  it  is  laid,  and 
during  this  period  it  should  be  carefully  watched  and  any 
needed  repairs  attended  to  at  once.  The  green  road  may  rut 
slightly  under  heavy  traffic  and  even  when  constructed  with  the 
greatest  care  is  apt  to  develop  weak  places.  Unless  these  are 
repaired  at  once  they  serve  as  starting  points  for  rapid 
disintegration.  After  the  road  has  once  seasoned,  however, 
there  is  much  less  cause  for  apprehension,  and  from  then  on  the 
cost  of  maintenance  should  be  much  less  than  for  ordinary 
macadam. 

Repairs  should  be  made  by  cutting  out  all  defective  places 
for  a  depth  of  about  two  inches  as  shown  in  Fig.  35.  The  holes 
should  have  sharp  vertical  sides  which  are  smeared  with  hot 
bitumen.  The  old  stone  is  replaced  with  fresh  bituminous 
concrete  and  the  patch  tamped  even  with  the  surrounding  road 
surface. 

Character  of  Aggregate  for  Bituminous  Macadam.  —  Bitumi- 
nous macadam  has  the  advantage  over  ordinary  macadam  of 
being  less  dependent  upon  the  quality  of  the  stone  for  good 
results,  and  many  rocks  which  are  unsatisfactory  for  the  latter 
may  be  used  to  advantage  in  this  class  of  work.  Thus  in 
straight  macadam  much  is  dependent  upon  the  cementing  value 
of  the  rock,  while  in  bituminous  macadam  this  factor  need  not 
be  considered,  as  the  bitumen  is  the  only  binder  to  be  taken  into 
account,  ^n  like  manner  rocks  which  are  deficient  in  hardness, 
toughness  and  resistance  to  wear,  from  the  standpoint  of  regular 
construction,  will  often  prove  serviceable  in  a  bituminous  mac- 
adam, as  they  are  protected  to  a  considerable  extent  from  the  wear 
and  tear  of  traffic  by  the  cushioning  effect  of  the  bitumen. 
By  this  is  not  meant  that  any  material  no  matter  how  soft  and 
crumbly  may  be  successfully  used,  but  only  that  much  lower 
standards  may  be  set.  Hard,  tough  rock  will  of  course  produce 
more  lasting  results  if  the  proper  binder  is  employed,  but  the 
softer  varieties,  such  as  limestone  and  dolomite,  may  often  prove 
satisfactory,  particularly  if  it  is  necessary  to  use  a  rather  fluid 


318  DUST   PREVENTIVES   AND    ROAD   BINDERS 

bitumen.  This  is  due  to  the  fact  that  the  greater  quantity 
of  the  fine  products  of  wear  are  mixed  with  the  binder  under 
traffic  and  increase  its  consistency  to  a  considerable  extent. 
In  England  blast  furnace  slag  has  been  successfully  employed 
in  the  construction  of  tarred-slag  macadam  and  some  few 
experiments  have  been  conducted  along  this  line  in  the 
United  States. 

Blast  furnace  slag  is  extremely  variable  in  its  physical  and 
somewhat  in  its  chemical  properties  even  when  taken  from  the 
same  furnace,  and  in  order  to  obtain  good  results  it  is  necessary  to 
exercise  some  care  in  selection.  Thus  according  to  its  composi- 
tion and  manner  in  which  it  is  cooled,  it  may  exist  as  a  dense  ar- 
tificial rock,  as  a  vitreous,  glassy  mass,  or  it  may  be  soft,  crumbly 
and  honeycombed.  Any  road  surface  composed  of  such  a 
heterogenous  mixture  will  wear  unevenly  and  it  is  therefore 
advisable  to  select  only  the  first  type  of  material  for  bituminous 
slag  surfaces.  Such  slag  is  easily  distinguishable  by  sight  from 
the  other  varieties  and  the  additional  expense  of  selecting  and 
sorting  this  material  before  it  goes  to  the  crusher  should  be  fully 
justified  by  the  better  and  more  lasting  character  of  the  road 
surface  of  which  it  is  composed.  It  would  seem  probable  that 
the  softer  and  more  crumbly  variety  could  be  utilized  to  ad- 
vantage if  crushed  to  the  size  of  screenings  to  serve  as  a  filler  for 
the  coarser  and  harder  fragments.  At  the  present  time,  too 
little  work  has  been  done  in  this  country  to  warrant  any  final 
judgment  as  to  the  best  practice  in  constructing  bituminous 
slag  macadam.  It  would  seem,  however,  that  this  type  of 
road  should  receive  considerable  attention  by  American  road 
engineers,  as  vast  mountains  of  slag  are  produced  in  this  country 
which  at  the  present  time  is  practically  waste  material  and, 
therefore,  much  cheaper  than  rock  in  localities  near  which  it 
is  produced. 

Patent  and  Proprietary  Bituminized  Aggregates.  —  In  Eng- 
land a  number  of  patent  and  proprietary  mixtures  of  bitumen 
with  various  mineral  aggregates  are  to  be  found.  These  mix- 
tures are  prepared  at  a  central  plant  from  which  they  are  shipped 


TAR   AND   CONSTRUCTION   OF   BITUMINOUS    MACADAM       319 

to  the  consumer  ready  for  application  to  the  road.  They  are 
laid  cold  and  for  this  reason  a  bitumen  of  softer  consistency 
than  is  desirable  for  construction  work  is  used  in  order  that  the 
concrete  may  be  handled  and  laid  without  difficulty.  "  Tarmac  " 
and  "Quarrite"  are  perhaps  the  most  widely  known  preparations 
of  this  nature,  and  have  been  used  with  some  degree  of  success. 
A  brief  description  of  the  former  will  give  some  idea  of  the  gen- 
eral character  of  these  preparations. 

Tarmac  consists  of  crushed  blast  furnace  slag  coated  while 
hot  with  a  tar  preparation  composed  of  tar,  pitch,  Portland 
cement  and  resin  in  substantially  the  following  porportions : 

Tar 92 . 56%  by  weight 

Pitch 5 . 79%  by  weight 

Portland  cement 41%  by  weight 

Resin i .  24%  by  weight 

In  the  preparation  of  this  compound  the  tar  is  first  heated  to 
1 00°  C.  and  the  other  ingredients  added  and  thoroughly  mixed. 
It  is  then  employed  as  a  coating  for  dry  or  warm  slag,  the  con- 
crete being  prepared  in  a  steam  jacketed  mixer.  The  slag  is 
crushed  and  screened  into  three  sizes  and  in  some  cases  is  taken 
directly  from  the  blast  furnace  while  it  is  still  hot.  The  pre- 
pared concrete  may  be  stored  for  some  time  before  using. 

The  Tarmac  road  is  built  in  a  manner  quite  similar  to  an  or- 
dinary macadam  except  that  of  course  no  water  is  used.  Three 
courses  of  tarred  slag  are  laid  and  rolled  separately.  For  the 
bottom  course  two  and  one-half  inch  gauge  is  employed,  for  the 
wearing  surface  one  inch  gauge,  and  on  top  of  this  a  course  of 
tarred  slag  sand  or  screenings.  All  of  the  road  metal  is,  there- 
fore, covered  with  tar.  While  this  is  by  no  means  an  objection- 
able feature,  it  raises  the  cost  to  over  double  that  of  an  ordinary 
macadam  even  in  places  where  the  material  is  prepared  and  used 
at  the  same  place.  It  is  probable  that  nearly  if  not  equally  as 
satisfactory  results  could  be  obtained  by  using  only  a  two  inch 
wearing  surface  of  the  tarred  slag  laid  upon  an  ordinary  broken 
stone  foundation. 


320  DUST   PREVENTIVES   AND    ROAD   BINDERS 

Walker  Smith,  in  his  treatise  on  tar  macadam,  expresses  his 
opinion  of  Tarmac  as  follows,  and  this  may  perhaps  be  taken  as 
representing  the  English  idea  of  this  material. 

"Much  has  been  heard  of  'Tarmac'  and  much  has  been 
claimed  for  it,  and  the  author  must  admit  that  when  he  first 
tried  'Tarmac'  as  an  experiment,  before  visiting  their  works, 
he  was  a  little  prejudiced  against  it,  principally  on  account  of 
the  variability  of  the  slag  and  to  some  extent  on  account  of 
the  specification  of  the  matrix  appearing  to  lend  itself  to  much 
variation  in  quality;  but  he  has  found  that  it  wears  evenly  and 
is  very  much  more  economical  than  granite  macadam,  but  that 
it  wears  more  rapidly  than  granite  tar  macadam." 

In  the  United  States  ready  prepared  bituminous  concretes 
for  use  in  road  work  have  been  but  recently  exploited.  Of  these 
two  may  be  mentioned,  "Warrenite"  and  "Amiesite."  The 
former  is  a  modification  of  the  well  known  "Bitulithic"  con- 
crete, the  latter  is  a  patented  preparation  made  by  coating  cold 
crushed  stone  with  a  fluid  asphaltic  cement,  and  lime.  "  Ami- 
esite "  is  prepared  at  the  quarry,  and  to  facilitate  handling  and 
prevent  solidification  of  the  concrete  before  being  laid,  about 
one-half  peck  of  dampened  sand  is  mixed  with  each  cubic  yard 
of  the  bitumen  covered  stone.  This  material  is  said  to  sell  for 
about  $3.50  per  cubic  yard  at  the  quarry.  It  is  laid  and  rolled 
cold  to  any  desired  depth,  either  upon  an  old  roadbed  which 
has  been  reshaped  or  upon  a  new  foundation  of  broken  stone. 
At  the  present  time  none  of  the  roads  constructed  of  " Amiesite" 
have  been  down  for  a  sufficiently  long  time  to  warrant  an  opinion 
of  its  serviceability.  The  author  has  had  occasion  to  examine 
a  very  small  section  cut  from  such  a  roadway,  mainly  for  the 
purpose  of  ascertaining  the  percentage  of  bitumen  and  lime. 
While  this  examination  is  very  incomplete,  owing  to  the  small- 
ness  of  the  sample,  it  is  given  below  for  the  purpose  of  showing 
the  general  characteristics  of  this  material. 


TAR   AND   CONSTRUCTION    OF   BITUMINOUS    MACADAM      32! 

AMIESITE. 


Character. 


Bitumen  Coated 

Mineral 
Aggregate. 


Soluble  in  CS2  (total  bitumen) 

Specific  gravity  extracted  bitumen  25°/25°  C. 
Per  cent  bitumen  insoluble  in  86°  naphtha.. . 

Per  cent  ash  in  extracted  bitumen 

Lime  CaO  (basis  of  mineral  matter) 

Lime  CaO  (basis  of  bitumen) 


Per  cent. 

5.68 

1.004 

22.46 

2.88 

•54 


Remarks.  —  This  material  would  seem  to  be  a  mineral  aggregate  coated  with  a 
soft  asphaltic  cement  and  lime.  The  ash  obtained  from  this  cement  indicates  the 
presence  of  a  native  asphalt  which  has  been  fluxed  with  a  considerable  quantity 
of  a  heavy  residual  oil. 

Before  leaving  the  subject  of  ready  prepared  bituminized 
aggregates,  mention  may  be  made  of  a  process  invented  by 
J.  C.  Travilla.  In  brief  this  process  consists  in  manufacturing 
lightly  compacted  slabs  of  a  mixture  of  bitumen,  sand,  and  stone 
particles  and  dust  in  such  proportion  that  the  slab  will  main- 
tain its  shape  while  being  handled  and  transported,  but  will  be 
sufficiently  soft  or  plastic  to  permit  it  to  be  squeezed  into  the 
voids  of  a  newly  laid  macadam  wearing  course.  This  layer  of 
stone,  ranging  in  size  from  one-half  to  two  and  one-half  inches, 
is  laid  upon  any  suitable  foundation  and  is  lightly  rolled.  Over 
this  is  spread  a  thin  coating  of  sand  or  fine  stone  screenings  in 
sufficient  quantity  to  partially  fill  the  voids.  A  coat  of  bitumi- 
nous cement  is  applied  over  the  surface  thus  formed  and  the 
slabs  then  laid  close  together,  as  shown  in  Fig.  36,  and  given  a 
preliminary  rolling  sufficient  to  squeeze  the  under  portion  into 
the  surface  below.  A  coating  of  bituminous  cement  is  then 
applied  and  covered  with  a  thin  coat  of  sand  or  screenings,  after 
which  the  road  is  rolled  until  smooth  and  firm.  Under  this 
final  rolling  it  is  claimed  that  the  slabs  are  welded  together  to 
form  a  continuous  surface.  This  type  of  road  is  in  effect  much 
like  that  of  the  rock  asphalt  macadam  described  on  page  225. 

Summary  and  Conclusions.  —  In  this  chapter  the  author  has 
described  the  application  of  various  kinds  of  tar  to  macadam  road 


322  DUST  PREVENTIVES   AND   ROAD   BINDERS 


en 

3 
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s 

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, 

JS 


TAR   AND   CONSTRUCTION   OF  BITUMINOUS    MACADAM    323 

surfaces  and  the  construction  of  bituminous  macadam  roads 
in  general.  The  character  and  use  of  representative  types  of 
patented  bituminous  concretes  have  also  been  discussed.  It  is 
probable  that  the  use  of  the  latter  will  always  be  restricted  to 
within  a  few  hundred  miles  of  the  neighborhood  in  which  they 
are  produced,  owing  to  heavy  freight  rates  on  their  90  or  more 
per  cent  of  mineral  matter,  which  makes  it  impossible  for  them 
to  successfully  compete  at  a  distance  with  the  concentrated 
bituminous  binders  and  local  road  stone.  There  is  no  reason, 
however,  why  the  average  road  engineer  should  not  prepare  his 
own  bituminous  concrete  and  in  many  cases  any  sort  of  binder 
which  he  desires  to  use,  by  means  of  mixing  machines  especially 
adapted  for  the  purposes  mentioned,  some  of  which  have  been 
described  above. 

"  While  the  mixing  method  is  undoubtedly  superior  to  the 
penetration  method  of  construction,  the  latter  may  often  be 
employed  to  advantage  for  roads  not  subjected  to  excessively 
heavy  traffic.  ^For  very  heavy  highway  traffic  the  mixing 
method  should  be  followed,  and  as  has  been  mentioned  earlier 
in  this  book,  it  is  probable  that  the  road  of  the  future  will  con- 
sist of  a  mixed  bituminous  concrete  wearing  surface  placed  upon 
a  cement  concrete  foundation.  )  Roads  requiring  this  type  of 
foundation  will  also  require  a  very  dense  and  strongly  bound 
wearing  surface.  Considerable  attention  will  have  to  be  given 
to  the  grading  of  the  aggregate  and  only  the  most  powerful 
forms  of  bituminous  road  binders  will  be  used.  At  the  present 
time  there  is  no  need  for  this  form  of  construction  except  in  very 
thickly  settled  districts  surrounding  some  of  our  large  cities, 
and  the  author  believes  that  by  the  exercise  of  a  little  judgment 
in  selection  the  road  engineer  may  obtain  very  satisfactory 
results  by  following  the  methods  described  in  this  chapter. 


CHAPTER  XIII. 

THE  EXAMINATION  OF  BITUMINOUS  ROAD  MATERIALS  AND 
INTERPRETATION  OF  RESULTS. 

IT  is  to  be  regretted  that  at  the  present  time  great  lack  of 
uniformity  exists  in  the  methods  of  examining  bituminous  road 
materials,  as  adopted  by  various  chemists.  The  subject  being 
closely  allied  to  the  examination  of  asphalts  and  asphaltic 
cements  employed  in  the  paving  industry,  a  very  natural  tend- 
ency has  been  exhibited  to  make  use  of  the  methods  already 
established  for  such  products.  The  same  criticism,  however, 
applies  to  the  examination  of  these  materials,  for  in  spite  of 
numerous  attempts  to  standardize  methods,  but  comparatively 
few  tests  are  to-day  made  in  exactly  the  same  manner  by  all 
laboratories  devoted  to  the  examination  of  paving  materials. 
For  a  number  of  years  a  special  committee  of  the  American 
Society  for  Testing  Materials,  composed  of  some  of  the  most 
prominent  workers  in  this  field,  has  been  engaged  in  the  problem 
of  standardizing  methods,  with  but  poor  success.  During  the 
past  year  this  committee  devoted  some  time  to  the  considera- 
tion of  standard  tests  for  bituminous  road  materials,  and  at  the 
twelfth  annual  meeting  of  the  Society,  during  the  summer  of 
1909,  proposed  certain  tentative  tests  for  these  materials,  which 
were  not,  however,  for  the  time  being  to  be  adopted  as  stand- 
ard. About  the  same  time,  at  a  meeting  of  the  board  of  directors 
of  the  American  Society  of  Civil  Engineers,  a  special  committee 
of  engineers  was  appointed  "To  Report  on  Bituminous  Materials 
for  Use  in  Road  Construction,  and  on  Standards  for  their  Test 
and  Use."  A  list  of  analyses  and  tests  was  formulated  by  the 
committee  and  sent  to  those  interested,  requesting  them  to 
make  such  suggestions  as  seemed  advisable  and  to  submit  them 
to  the  committee,  which  would  then  make  whatever  changes 

324 


EXAMINATION    OF   BITUMINOUS    ROAD    MATERIALS       325 

it  deemed  necessary  before  advocating  the  analyses  and  tests 
as  standard. 

Both  the  proposed  tests  of  the  American  Society  for  Test- 
ing Materials  and  the  revised  list  of  Standard  Tests  of  the 
American  Society  of  Civil  Engineers  are  given  in  Chapter  XIV 
for  the  sake  of  those  who  may  desire  to  refer  to  or  use  them. 
It  is  not  the  author's  purpose  here  to  consider  the  relative 
merits  and  objectionable  features  of  each,  but  to  describe  and 
discuss  in  some  detail  tests  which  from  his  experience  he  deems 
most  useful  as  applied  to  bituminous  road  materials.  The 
majority  of  these  tests  are  at  present  employed  in  the  labora- 
tory of  the  United  States  Office  of  Public  Roads,  and  have  been 
selected  as  most  applicable  to  the  great  variety  of  materials 
from  all  parts  of  the  United  States  which  are  there  examined. 
It  is  realized  that  in  view  of  the  comparative  newness  of  the 
subject  no  one  set  of  tests  can  at  present  be  selected  which  is 
above  criticism,  and  it  is  most  certain  that  methods  will  have 
to  be  changed  or  modified  from  time  to  time  to  meet  new  con- 
ditions as  they  arise.  All  tests  are  not  equally  applicable  to 
all  classes  of  bituminous  compounds,  and  this  is  particularly 
true  of  tars  as  compared  with  oils  and  asphalts,  as  will  appear 
later. 

Value  of  Examination.  —  Although  in  the  past  the  ex- 
amination of  bituminous  road  materials  has  been  sadly  neg- 
lected, it  is  now  generally  admitted  that  such  examinations 
are  very  necessary  for  the  intelligent  selection  and  use  of  these 
materials.  Realization  that  many  experiments  have  proved 
unsuccessful  because  the  experimenter  had  no  knowledge  of 
the  physical  and  chemical  characteristics  of  the  binder  which 
he  used  has  awakened  considerable  interest  in  the  testing  of 
bituminous  road  materials.  The  old  idea  that  an  oil  is  simply 
an  oil,  and  if  it  has  produced  good  results  in  one  locality 
should  produce  equally  good  results  in  another,  has  given  place 
to  the  knowledge  that  great  variations  exist  in  the  road  build- 
ing properties  of  different  oils,  and  that  not  only  will  results 
depend  upon  the  peculiar  characteristics  of  a  given  material,. 


326  DUST   PREVENTIVES   AND    ROAD   BINDERS 

but  that  the  method  of  application  and  local  conditions  to 
which  it  is  subjected  are  most  important  factors  to  be  con- 
sidered. The  same  is,  of  course,  true  of  tars  and  any  other 
class  of  bituminous  binders. 

When  making  an  examination  a  number  of  factors  should  be 
considered,  which  may  often  modify  the  method  to  some 
extent.  Those  of  most  importance  are  as  follows: 

(1)  Purpose  for  which  the  material  is  to  be   used,    i.e.,    as 
a  dust  preventive  only,  as  a  semipermanent  binder  and  dust 
preventive  for  surface  treatment,  or  as  a  permanent  binder  in 
construction  work. 

(2)  Character  of  the  road  to  be  treated,  including  the  type 
of  road  (earth,  gravel,  or  broken  stone)  and  the  physical  char- 
acteristics of  the  road  material. 

(3)  Desired  method  of  application,  i.e.,  whether  the  material 
is  to  be  applied  cold  or  hot  and  by  means  of  a  sprinkler,  with 
or  without  pressure,  by  pouring  from  buckets,  or  as  a  prepared 
mixture  with  the  road  material.     In  the  latter  case  it  is  also 
desirable  to  know  whether  or  not  the  road  material  itself   is 
to  be  heated. 

(4)  Quantity  and  character  of  traffic. 

(5)  Climatic  conditions. 

When  these  facts  are  known,  the  examination  becomes  of 
more  value  than  simply  a  means  of  identification.  In  any 
event,  however,  it  serves  the  latter  purpose,  and  even  if  an 
experimenter  cannot  interpret  the  results  of  an  examination, 
he  can  use  them  as  a  guide  in  duplicating  his  work  under  a 
given  set  of  conditions.  Thus  if  in  his  work  he  has  found  that 
good  results  have  been  obtained  from  the  use  of  a  bitumen 
having  a  certain  specific  gravity,  a  certain  penetration,  a  cer- 
tain melting  point,  certain  chemical  characteristics,  etc.,  he 
can  be  reasonably  sure  of  duplicating  these  results  with  another 
lot  of  material  showing  the  same  characteristics. 

Any  one  characteristic  will  not,  of  course,  indicate  the  suit- 
ability of  a  bituminous  binder  for  road  purposes,  and  it  is  only 
by  considering  its  collective  characteristics  that  a  satisfactory 


EXAMINATION    OF   BITUMINOUS    ROAD   MATERIALS       327 

idea  of  its  value  for  this  purpose  can  be  ascertained.  This  is 
particularly  noticeable  when  comparing  oils  and  tars.  Thus 
for  construction  work  an  oil  product  having  a  specific  gravity 
of  i. 08  might  be  entirely  satisfactory,  while  a  tar  having  the 
same  specific  gravity  could  never  be  suitable  for  such  work. 

Because  of  the 'very  great  difference  between  oils  and  tars, 
somewhat  different  methods  of  examination  are  followed.  A 
summary  of  the  most  important  tests  for  each  are  given  at  the 
conclusion  of  this  chapter. 

General  Characteristics.  —  When  making  an  examination  of 
any  kind  of  bituminous  binder  it  is  well  to  note  its  general 
characteristics,  such  as, — 

(1)  Color  by  reflected  and  transmitted  light. 

(2)  Odor. 

(3)  Feel  (i.e.,  whether  sticky  or  greasy). 

(4)  Whether  smooth  or  granular. 

(5)  Physical  state  at  normal  temperature  (fluid,  semisolid,  or 
solid). 

While  it  is  difficult  to  describe  the  differences  in  such  char- 
acteristics of  various  types  of  bituminous  materials,  it  is  often 
possible  for  one  who  has  acquired  some  experience  in  handling 
and  testing  them  to  obtain  by  this  means  a  fair  idea  of  the 
kind  of  bitumen  which  is  to  be  further  examined.  Crude  oils 
are  usually  lighter  in  color  and  have  a  different  odor  from 
residual  oils,  besides  being  more  fluid.  Tars  are  darker  in  color 
than  the  oils  and  have  a  characteristic  odor  which  is  unmistak- 
able and  readily  distinguishes  them  from  the  former.  In  mix- 
tures of  oil  and  tar  it  is  often  possible  to  distinguish  the  odor  of 
each,  especially  if  the  product  is  warmed.  Crude  tars  have  a 
strong  gassy  odor,  which  is  not  so  noticeable  in  refined  products. 
Tars  are  as  a  rule  more  sticky  than  oils,  and  the  asphaltic  oils 
more  sticky  than  those  of  a  paraffin  nature  when  of  approxi- 
mately the  same  consistency.  Tar  products  that  are  lumpy  or 
granular  contain  an  excess  of  free  carbon,  and  this  property  in  oils 
is  indicative  of  a  considerable  amount  of  paraffin  scale.  Many 
other  differences  might  be  cited,  but  as  they  are  all  only  relative 


328  DUST   PREVENTIVES   AND    ROAD   BINDERS 

they  serve  as  an  indication  only,  and  not  as  proof  of  the  kind 
of  material  under  examination. 

Specific  Gravity.  —  (Method.)  This  determination  should 
be  made  upon  all  types  of  bituminous  road  materials.  The 
temperature  at  which  the  specific  gravity  is  taken  should  always 
be  stated,  in  making  a  report.  For  most  purposes  it  will  be 
found  convenient  to  make  the  determination  at  25°  C.  and  to 
express  the  results  as  compared  with  water  at  the  same  tempera- 
ture. This  is  indicated  in  a  report  by  the  sign  25°/25°  C. 
Some  analysts  prefer  to  report  the  specific  gravity  in  degrees 
Baume.  The  author  prefers  the  direct  system,  and  all  specific 
gravities  given  in  this  book  are  based  upon  water  taken  as 
i.ooo.  Baume  tables  of  specific  gravity  are,  however,  given  in 
the  appendix  for  the  use  of  those  who  wish  to  transpose  from  one 
scale  to  the  other. 

(a.  Hydrometer.)'  The  most  convenient  method  of  deter- 
mining the  specific  gravity  of  very  fluid  bitumens  is  by  means  of 
a  thin  spindle  hydrometer.  These  hydrometers,  graduated  in 
direct  specific  gravity  readings,  may  be  obtained  from  any  dealer 
in  chemical  apparatus  at  small  cost,  either  singly  or  in  sets. 
One  ranging  from  i.ooo  to  1.200  is  most  suitable  for  tars,  while 
a  set  ranging  from  0.7000  to  i.ooo  will  be  found  useful  for  oils. 
When  the  bitumen  is  too  viscous  to  allow  the  hydrometer,  to 
settle  properly  a  pycnometer  may  be  employed.  One  suitable 
for  general  use  is  described  below.  In  some  instances  very 
viscous  materials  are  heated  up  to  a  point  of  sufficient  fluidity 
and  their  specific  gravity  then  taken  with  a  hydrometer,  the 
temperature  at  which  the  determination  is  made  being  noted. 
This  practice  is  largely  followed  by  oil  chemists,  who  by  means 
<of  tables  calculate  the  specific  gravity  at  any  desired  temperature. 
The  method  is  not  accurate  for  the  determination  of  all  types  of 
bitumen,  owing  to  variations  in  their  coefficients  of  expansion.. 

(b.  Pycnometer.)  The  inconvenience  and  difficulty  of  em- 
ploying the  ordinary  narrow-neck  pycnometer  when  determining 
the  specific  gravity  of  dense  residual  oils  and  soft  tar  pitches  has 
led  the  author  to  devise  a  modified  form  suitable  for  use  in  this 


EXAMINATION   OF   BITUMINOUS    ROAD   MATERIALS      329 


connection.  Except  in  cases  where  extreme  accuracy  is  desired, 
this  pycnometer  is  also  suited  for  determinations  of  non- volatile 
oils,  especially  those  -  of  too  high  viscosity  for  use  with  the 
Westphal  balance  or  hydrometer. 

The  pycnometer,  as  shown  in  Fig.  37,  consists  of  a  fairly  heavy, 
straight- walled  glass  tube,  70  mm.  long  and  22  mm.  diameter, 
ground  to  receive  a  solid  glass  stopper  with  a  1.6  mm.  bore  in 
place  of  the  usual  capillary  opening.  The  lower  part  of  this 
stopper  is  made  con- 
cave in  order  to  allow 
all  air  bubbles  to  escape 
through  the  bore.  The 
depth  of  the  cup-shaped 
depression  is  4.8  mm.  at 
the  center.  The  stop- 
pered tube  has  a  capac- 
ity of  about  24  cc.  and 
when  empty  weighs 
about  28  gms.  Its  prin- 
cipal advantages  are, 
that  (i)  any  desired 
amount  of  bitumen  may  FIG.  37.  Pycnometer  for  Determining  the 
be  poured  in  without  Specific  Gravity  of  Bituminous  Road 

,  .      ,,       .  ,        ,  Materials, 

touching  the  sides  above 

the  level  desired;  (2)  it  is  easily  cleaned;  (3)  on  account  of  the 
TV  inch  bore  the  stopper  can  be  more  easily  inserted  when  the 
tube  is  filled  with  a  very  viscous  oil  than  if  it  contained  a 
capillary  opening. 

When  working  with  semisolid  bitumens  which  are  too  soft  to 
break  and  handle  in  fragments,  the  following  method  of  deter- 
mining their  specific  gravity  has  been  employed  by  the  author 
with  good  results.  The  clean,  dry  pycnometer  is  first  weighed 
empty  and  this  weight  called  "a."  It  is  then  filled  with  freshly 
distilled  water  at  25°  C.  in  the  usual  manner,  the  weight  again 
taken  and  called  "b."  The  bitumen  should  be  brought  to  a 
fluid  condition  by  the  gentle  application  of  heat,  care  being  taken 


330  DUST   PREVENTIVES   AND    ROAD   BINDERS 

that  no  loss  by  evaporation  occurs.  When  sufficiently  fluid 
enough  is  poured  into  the  pycnometer,  which  may  also  be 
warmed,  to  about  half  fill  it,  without  allowing  the  material  to 
touch  the  sides  of  the  tube  above  the  desired  level.  If  the 
presence  of  air  bubbles  is  suspected,  the  tube  may  then  be 
placed  for  a  few  minutes  in  a  vacuum  chamber  made  by  invert- 
ing a  large  glass  funnel  on  a  ground-glass  plate,  as  shown  in 
the  figure,  the  edge  of  the  funnel  being  smeared  with  desiccator 
grease.  After  all  air  bubbles  have  thus  been  removed,  the  tube 
and  contents  are  cooled  to  25°  C.  in  any  suitable  manner  and 
weighed  with  the  stopper.  This  weight  is  called  "c."  Dis- 
tilled water  at  25°  C.  is  then  poured  in  until  the  pycnometer  is 
full,  the  stopper  inserted  and  the  whole  weighed.  This  weight  is 
called  "d."  From  the  weights  obtained,  the  specific  gravity 
of  the  bitumen  may  be  readily  calculated  from  the  following 
formula : 

Specific  gravity  25°/25°  C 


(b-a)-(d-c) 

Both  "  a  "  and  "  b  "  are  constants  and  need  not  be  determined 
but  once.  It  is  therefore  necessary  to  make  only  two  weighings 
for  all  determinations  after  the  first.  Results  obtained  according 
to  the  above  method  are  accurate  to  within  two  units  in  the  third 
decimal  place  as  compared  with  the  open-tube  method  commonly 
employed,  which  is  accurate  to  the  second  decimal  place  only. 

The  specific  gravity  of  fluid  bitumens  may  be  determined  in 
the  ordinary  manner  with  this  pycnometer  by  completely  filling 
it  with  the  material  and  dividing  the  weight  of  the  bitumen 
thus  obtained  by  that  of  the  same  volume  of  water. 

The  pycnometer  may  be  readily  cleaned  by  placing  it  in  a  hot- 
air  bath  until  the  bitumen  is  sufficiently  fluid  to  pour.  As 
much  is  drained  out  as  possible  and  the  interior  swabbed  with  a 
piece  of  cotton  waste.  It  is  then  rinsed  clean  with  a  little 
carbon  bisulphide,  and  after  drying  is  again  ready  for  use. 

(Sommer's  method.)  A  method  of  determining  the  specific 
gravity  of  asphalts  and  semisolid  substances  which  deserves 


EXAMINATION   OF  BITUMINOUS    ROAD   MATERIALS       33! 


notice  has   recently  been   devised  by  Sommer*  who  describes 
the  method  as  follows: 

"The  main  feature  of  the  method  is  to  let  the  asphalt  chill 
in  a  small  cylindrical  vessel  which  is  divided  into  two  parts, 
the  lower  holding  exactly  10  cc.,  and  the  upper  being  removable 
from  the  cup  by  the  connecting  thread."  (See  Fig.  38.)  "The 
principle  of  the  instrument  is  to  have  the  shrinkage  take  place  in 


SLEEVE 


CUP 


FLANGE 


COVER 


FIG.  38.     Sommer's  Specific  Gravity  Apparatus. 

the  upper,  removable  sleeve,  so  that  after  the  removal  of  the 
same  the  lower  cup  contains  a  certain  fixed  volume. 

"The  entire  vessel  is  filled  with  melted  asphalt  and  heated 
for  a  little  while  at  a  temperature  slightly  above  the  melting 
point,  in  order  to  thoroughly  remove  air  bubbles  or  traces  of 
water.  After  the  surface  is  clear,  the  vessel  is  allowed  to  cool, 

*  "  Proc.  Am.  Soc.  for  Test.  Mat.,"  Vol.  IX,  1909. 


332  DUST   PREVENTIVES   AND   ROAD   BINDERS 

at  first  in  air  (to  avoid  sudden  contraction  and  hence  separation 
of  the  asphalt  from  the  sides  of  the  tube),  and  then  in  water  of 
the  desired  temperature,  which  will  usually  be  60°  F.  The 
sample  should  be  left  in  the  water  a  sufficient  time  to  thoroughly 
adopt  its  temperature,  and  a  half  hour  will  not  be  too  long 
for  this  purpose.  Then  it  is  removed. from  the  water,  wiped 
dry,  and  the  upper  extension  part  or  "sleeve"  is  removed.  If 
the  asphalt  is  so  hard  that  it  renders  the  unscrewing  difficult,  the 
upper  part  should  be  warmed  with  a  Bunsen  burner.  The 
sleeve  is  then  pulled  off  and  the  asphalt  which  extends  above 
the  level  of  the  cup  is  cut  off  with  a  broad  knife. 

"The  cup  will  then  contain  exactly  10  cc.  of  asphalt  at  60°  F. 
This  quantity  can  be  directly  weighed  on  an  analytical  balance, 
and  the  specific  gravity  ascertained  by  dividing  the  number  of 
grams  of  asphalt  by  ten.  The  following  method,  however, 
simplifies  the  procedure: 

"After  the  cup  is  filled  flush,  a  cover  is  slid  on  it  from  the 
side,  and  fastened  to  it  by  a  flange."  .  .  .  "The  cup  and  its 
contents  are  then  suspended  from  a  special  hydrometer  and 
the  whole  instrument  is  placed  in  a  jar  containing  water  at 
60°  F."  ...  "If  any  air  bubbles  form  on  the  instrument,  it 
should  be  twisted  once  or  twice  quickly  and  they  will  escape. 
The  specific  gravity  can  then  be  read  directly  on  the  stem  of 
the  hydrometer  without  correction." 

The  inventor  claims  that  this  method  is  accurate  to  the 
third  decimal  place  and  that  it  is  reliable  for  oils  and  other 
semiliquids. 

(Interpretation  of  results.)  The  specific  gravity  determination 
as  noted  in  the  above  methods  is  made  upon  both  oils  and  tars.  It 
is  of  value  mainly  as  a  means  of  identification,  but  when  consid- 
ered in  connection  with  other  tests  is  often  of  service  in  deter- 
mining the  suitability  of  the  material  for  road  purposes.  As 
applied  to  oil  and  oil  products,  the  specific  gravity  is  a  rough  in- 
dication of  the  amount  of  heavy  hydrocarbons  which  give  body 
to  the  material.  Crude  petroleums  vary  in  specific  gravity  from 
0.73  to  0.98  and  slightly  higher,  paraffin  oils  as  a  rule  having 


EXAMINATION    OF    BITUMINOUS    ROAD    MATERIALS      333 

the  lowest  specific  gravity  and  asphalt  oils  the  highest.  The 
former  have  practically  no  value  for  road  work,  while  the  latter 
constitute  the  most  desirable  type.  Oils  containing  a  semi- 
asphaltic  base  hold  an  intermediate  position  and  will  usually 
run  higher  in  specific  gravity  than  the  paraffin  oils  and  lower 
than  the  truly  asphaltic  oils.  Solid  native  bitumens  free  from 
mineral  matter  usually  have  a  specific  gravity  of  not  over 
1.04.  If  the  specific  gravity  of  an  oil  product  or  asphalt  runs 
higher  than  this,  the  presence  of  mineral  matter  is  indicated 
and  in  native  asphalts  the  increase  is  almost  directly  propor- 
tional to  the  amount  of  mineral  matter  present,  except  when 
the  material  is  very  hard  and  brittle.  Thus,  a  specific  gravity 
of  1.40  indicates  the  presence  of  approximately  38  per  cent 
mineral  matter,  while  1.30  indicates  from  20  to  25  per  cent 
mineral  matter.  This  is,  of  course,  only  approximately  true,  as 
the  specific  gravity  of  the  asphalt  is  not  only  dependent  upon  the 
character  and  consistency  of  the  bitumen  itself,  but  also  upon 
the  specific  gravity  of  the  mineral  matter  which  it  holds.  Any 
oil  having  a  specific  gravity  of  over  0.93  or  0.94  should  be  heated 
before  application  and  no  natural  or  residual  oil  having  a  spe- 
cific gravity  of  less  than  0.95  should  be  employed  as  a  perma- 
nent binder.  For  construction  work  those  lying  between  0.98 
and  i. oo  are  to  be  preferred.  If  a  native  asphalt  containing 
mineral  matter  has  been  fluxed  to  suitable  consistency  for  such 
work,  the  specific  gravity  may,  of  course,  run  considerably 
higher. 

Crude  coal  tars  vary  in  specific  gravity  from  i.io  to  1.25  and 
sometimes  higher,  while  crude  water  gas  tars  lie  between  i.oo 
and  i.io.  In  coal  tars,  the  specific  gravity  is  largely  depend- 
ent upon  the  percentage  of  free  carbon  or  soot  which  they  con- 
tain, those  of  low  specific  gravity  holding  but  .little  and  those 
of  high  specific  gravity  holding  a  large  amount  of  free  carbon. 
Thus  a  crude  tar  having  a  specific  gravity  of  less  than  1.15  will 
usually  show  less  than  12  per  cent  free  carbon,  while  those 
running  as  high  as  1.22  will  have  30  per  cent  and  over.  As 
free  carbon  is  detrimental  to  road  work,  tars  of  low  specific 


334 


DUST   PREVENTIVES   AND    ROAD    BINDERS 


gravity  are  as  a  rule  to  be  preferred.  Gas  house  tars  in  gen- 
eral are  heavier  than  coke  oven  tars,  produced  at  low  tempera- 
ture, as  they  carry  a  greater  percentage  of  free  carbon. 

In  working  upon  dehydrated  coal  tars  Kohler  *  found  the 
following  relations  to  exist  between  their  specific  gravity  and 
free  carbon  contents: 

DEHYDRATED    COAL    TARS. 


Origin  of  Tar. 

Specific 
Gravity. 

Free  Carbon, 
Per  cent. 

Heidelberg  

220 

2  •?    7C. 

Darmstadt  

2IC 

2O    Q3 

Baden-Baden 

TQC 

Bockenheim        

•  *y5 

IQO 

Frankfort    

1  80 

I  C    7O 

Bam  berg  

I  7C 

Ao  •  /u 

T  e    T  t 

Neustadt  

172 

AJ  •  xo 
I  C    O7 

Caunstadt 

T  A/I 

Rottweil 

161 

Karlsruhe 

Ulm  

•  ^DJ 

I  C.O 

1OO(J 

Heilbronn  

I  CO 

Oos  

14.  C 

5OO 

.  w<_> 

Determinations  of -the  relation  between  these  properties  in 
refined  tars  of  approximately  the  same  consistency,  made  in 
the  laboratory  of  the  Office  of  Public  Roads,  gave  the  following 
results: 

REFINED  TARS. 


Specific  Gravity. 

25°/25°  C. 

Free  Carbon, 
Per  cent 

.216  

MCA 

.  23O.  . 

18  6? 

.270  

20  10 

.  24<.  . 

^5  

.2C6.  . 

22     CO 

.262  

26    O2 

•273.  . 

28    76 

.284  

33    IO 

*  Zsch.  f.  angew.  ch.,  1888,  p.  677. 


EXAMINATION    OF   BITUMINOUS    ROAD    MATERIALS       335 


In  refined  tars  specific  gravity  naturally  increases  with  consist- 
ency, both  because  the  lighter  hydrocarbons  and  water  have 
been  removed  and  because  the  relative  proportion  of  free  carbon 
has  been  increased  in  the  residue.  In  such  products  for  a  given 
consistency  a  low  specific  gravity  is  to  be  preferred  to  a  high 
one.  This  is  not  true,  however,  when  considering  refined  prod- 
ucts of  different  consistencies,  as  in  such  cases  while  the  per- 
centage of  free  carbon  might  be  the  same,  the  most  desirable 
product  might  show  the  highest  specific  gravity  for  the  reasons 
mentioned  above. 

As  a  rule,  crude  tars  having  a  specific  gravity  higher  than 
1. 1 8  cannot  be  distilled  to  produce  satisfactory  road  binders, 
unless  previously  mixed  with  a  much  lighter  tar,  preferably  a 
water  gas  tar.  No  refined  tars  running  lower  than  1.16  should 
be  used  in  construction  work,  and  the  same  may  be  said  of 
those  running  higher  than  1.24.  The  lower  limit  is  set  from  the 
standpoint  of  consistency,  while  the  higher  is  based  upon  the 
free  carbon  contents.  Any  tar  hav- 
ing a  specific  gravity  greater  than 
1.15  should  be  heated  before  being 
applied.  Those  running  under  1.15, 
which  do  not  have  to  be  heated  be- 
fore application,  can  be  considered 
as  dust  layers  and  temporary  bind- 
ers only. 

Flash  and  Burning  Points.  - 
(Method.)  A  determination  of  the 
flash  point  and  burning  point  of 
road  oils  can  for  ordinary  purposes 
be  made  according  to  the  open  cup 
method.  For  this  determination 
the  author  employs  a  form  of 
apparatus  shown  in  Fig.  39,  known 
as  the  Cleveland  Oil  Tester.  This 


FIG.  39.    Cleveland  Oil  Tester. 


oil  tester  consists  of  a  brass  water  or  oil  bath  A  resting  upon 
the  stand  B  and  heated  by  means  of  the  Bunsen  burner  C. 


336  DUST   PREVENTIVES   AND    ROAD    BINDERS 

The  oil  to  be  tested  is  placed  in  the  brass  cup  D  and  the 
thermometer  E  adjusted  so  that  its  bulb  is  completely  covered 
with  the  oil.  For  very  low  flashing  oils  the  bath  is  filled 
with  water  or  a  non-volatile  oil,  but  for  high  flashing  prod- 
ucts this  space  is  left  empty.  Heat  is  applied  so  that  the 
temperature  of  the  oil  in  the  cup  is  raised  at  the  rate  of  about 
5°  C.  per  minute  and  from  time  to  time  a  small  flame,  about  the 
size  of  a  pea,  from  a  capillary  glass  or  metal  tube  is  passed  over 
the  oil  about  half  an  inch  from  the  surface.  The  temperature 
at  which  the  evolved  vapors  flash  is  noted  and  also  the  tem- 
perature at  which  the  oil  ignites  and  burns.  The  flame  should 
not  be  blown  out  at  the  conclusion  of  this  test  for  danger  of 
splashing  the  hot  oil.  A  cover  or  extinguisher  should  be  em- 
ployed for  this  purpose  by  placing  it  over  the  ignited  oil. 

(Interpretation  of  results.)  This  determination  is  of  value  as 
a  quick  means  of  differentiating  between  the  heavy  crude  oils 
and  cut-back  products,  and  the  fluid  residuums.  It  also  indi- 
cates the  point  to  which  a  refined  oil  has  been  distilled  and 
whether  or  not  it  is  advisable  to  heat  the  material  before  appli- 
cation. Crude  oils  have,  of  course,  a  lower  flash  point  than 
residual  oils  and  among  the  crude  oils  themselves  those  of  a 
paraffin  nature  usually  flash  at  a  lower  temperature  than  the 
asphaltic.  The  former  may  run  as  low  as  ordinary  tempera- 
ture, while  the  latter  are  sometimes  as  high  as  135°  C.  Some 
crude  asphaltic  oils  will,  however,  show  quite  as  low  flash  point 
as  the  paraffin  oils,  so  that  no  great  dependence  can  be  placed 
upon  this  difference  in  crude  petroleums.  The  flash  point  of 
residual  road  oils  commonly  exceeds  200°  C.,  while  that  of  cut- 
back products  will  vary  greatly,  according  to  the  flash  point  of 
the  flux  and  the  percentage  and  character  of  the  heavier  resid- 
ual product.  If  it  is  desired  to  cut  a  heavy  binding  base  with 
a  more  volatile  product,  a  determination  of  the  flash  and  burn- 
ing points  of  the  constituents  is  of  little  value  in  calculating 
those  of  the  mixture.  Sherman,  Gray,  and  Hammerschlag  * 
have  shown  that  these  properties  are  not  additive  and  that  the 

*  Jour,  of  Ind.  and  Eng.  Chem.,  Vol.  I,  No.  i,  p.  16. 


EXAMINATION   OF   BITUMINOUS    ROAD    MATERIALS       337 

differences  between  the  calculated  and  actual  results  increase 
with  the  differences  in  properties  of  the  two  products  which 
constitute  the  mixture.  The  following  results  obtained  by  the 
author  on  mixtures  of  a  petroleum  distillate  and  a  heavy  petro- 
leum residue  are  given  in  the  following  table.  In  these  experi- 
ments it  will  be  noted  that  there  is  but  little  difference  in  the 
flash  points  of  those  mixtures  carrying  from  ten  to  sixty  per  cent 
of  the  residue. 

FLASH  AND  BURNING  POINT  DETERMINATIONS. 


Sample  No. 

Character. 

Flash  Point,  • 
°C. 

Burning 
Point,  °C. 

o 
I 

2 

3 

4 

6 

8 
9 

10 

Petrole 

10%  N 

20% 

30% 
40% 
50% 
60% 
70% 
80% 
90% 

Petrole 

um  < 

0.    1C 

um  i 

iistillate. 
3,  90%  N 
80% 
70% 
60% 
50% 
40% 
30% 

20% 

10% 
"esidue 

100° 

143° 
144° 
144° 
144° 
146° 
148° 

159° 

178° 

210° 
2600 

155° 

0.    C 

)  

173° 

208° 

269° 
296° 

Viscosity.  —  (Method.)  The  viscosity  of  fluid  bituminous 
road  binders  may  be  determined  by  means  of  the  Engler  Vis- 
cosimeter  at  any  desired  temperature.  This  apparatus  is 
shown  in  Fig.  40,  and  may  be  described  as  follows:  A  is  a 
shallow  brass  vessel  for  the  reception  of  the  oil  which  may  be 
closed  by  the  cover  Av  To  the  conical  bottom  of  A  is  fitted 
the  outflow  tube  a,  exactly  20  mm.  long,  with  a  diameter  on 
top  of  2.9  mm.  and  on  the  bottom  of  2.8  mm.  This  tube  can 
be  closed  by  the  pointed,  hardwood  stopper  b,  and  opened  by 
withdrawing  the  latter.  Three  pointed  projections  c  are  placed 
at  equal  distances  from  the  bottom  and  serve  for  measuring 
the  charge  of  oil,  240  cc.  The  thermometer  t  serves  for  read- 
ing the  temperature  of  the  material  to  be  tested.  The  vessel 
A  is  surrounded  by  a  brass  jacket  BB,  open  on  top,  which  serves 
for  the  reception  of  a  heavy  mineral  oil  for  heating  the  con- 


338 


DUST   PREVENTIVES   AND    ROAD   BINDERS 


tents  up  to  any  desired  temperature.  For  temperatures  lower 
than  100°  C.  water  may  be  used  instead  of  the  oil.  For  observ- 
ing the  temperature  of  the  bath  a  thermometer  is  fixed  in  this 
medium.  A  tripod  D  serves  as  a  support  for  the  "whole  and 


FIG.  40.     Engler  Viscosimeter. 

also  carries  the  ring  burner  d,  by  means  of  which  the  bitumen 
is  brought  to  and  maintained  at  the  desired  temperature. 
Under  the  outflow  tube  stands  the  measuring  flask  C.  A  flask 
graduated  to  50  and  100  cc.  is  most  suitable  for  road  binders. 

To  work  with  this  apparatus  the  time  must  first  be  deter- 
mined which  is  required  by  water  at  25°  C.  running  from  it  to 
fill  a  given  volume.  The  viscosity  of  the  material  under  ex- 


EXAMINATION   OF   BITUMINOUS   ROAD   MATERIALS        339 

amination  is  then  determined  in  proportion  to  that  of  water  at 
25°  C.  Thus  if  24  seconds  are  required  for  100  cc.  of  water  to 
pass  through  the  outlet  tube,  and  120  seconds  for  the  material 

examined,  the  latter  would  have  a  specific  viscosity  of =  5. 

24 

The  test  is  made  as  follows:  The  oil  cup  and  outlet  tube 
are  scrupulously  cleaned,  the  stopper  inserted  in  the  tube  and 
the  cup  filled  with  the  road  binder,  to  the  mark  indicated. 
The  cover  is  then  placed  in  position  and  the  material  brought 
to  and  maintained  at  the  desired  temperature  for  at  least  three 
minutes.  The  stopper  is  then  withdrawn  and  the  time  re- 
quired to  fill  the  measuring  flask  to  the  desired  mark  is  ascer- 
tained by  means  of  a  stop  watch. 

(Value  of  test.)  If  for  any  reason  it  is  desired  to  apply  a 
road  binder  at  a  given  temperature,  as  for  instance  when  it  is 
to  be  heated  by  means  of  steam,  a  determination  of  its  vis- 
cosity at  that  temperature  is  often  of  value.  The  test  also 
serves  as  a  means  of  identification.  The  viscosity  of  tars  con- 
taining appreciable  quantities  of  free  carbon  cannot  be  ac- 
curately determined  with  this  instrument,  owing  to  the  clogging 
effect  of  the  suspended  particles.  When  a  viscous  material  is 
to  be  cut  with  one  of  lower  viscosity  in  order  to  bring  it  to  a 
proper  consistency  for  application,  the  actual  viscosity  of  the 
mixture  should  be  ascertained  and  not  calculated  from  that  of 
the  two  constituents  for  the  reason  that  this  property  is  not 
additive,  as  has  been  shown  in  the  same  paper  referred  to  under , 
the  flash  point  and  burning  tests. 

Float  Test.  —  (Method.)  For  materials  which  are  very  vis- 
cous the  float  test  may  be  employed  as  a  measure  of  their  con- 
sistency. The  apparatus  used  is  known  as  the  New  York 
Testing  Laboratory  Float  Apparatus.  It  is  described  by 
Forrest*  as  follows:  "The  apparatus,  which  is  made  by 
Howard  &  Morse,  Brooklyn,  N.  Y.,  consists  of  two  parts,  an 
aluminum  float  or  saucer,  and  a  conical  brass  collar.  The  two 
parts  are  shown  in  the  drawing,"  (see  Fig.  41)  "and  are  made 

*  Eng.  Rec.,  Vol.  59,  p.  584. 


340 


DUST   PREVENTIVES    AND    ROAD    BINDERS 


separately  for  reasons  of  economy,  so  that  one  or  two  of 
the  floats  will  be  sufficient  for  an  indefinite  number  of  brass 
collars. 

"In  using  the  apparatus,  the  brass  collar  is  placed  upon  a 

brass  plate,  the  surface 
of  which  has  been  amal- 
gamated, and  filled  with 
the  bitumen  under  ex- 
amination, after  it  has 
been  softened  sufficiently 
to  flow  freely  by  gentle 
heating.  The  collar  must 
be  level-full,  and  as  soon 
as  the  bitumen  has  cooled 
sufficiently  to  handle,  it 
is  placed  in  ice  water  at 
41°  F.  for  15  minutes. 
It  is  then  attached  to  a 
float  and  immediately 
placed  upon  the  surface 
of  the  water,  which  is 
maintained  at  90°  F.  or 
any  other  temperature 
desired. 

"As  the  plug  of  bitu- 
men in  the  brass  collar 
becomes  warm  and  fluid, 
it  is  gradually  forced  out 
of  the  collar,  and  as  soon 
as  the  water  gains  en- 
trance to  the  saucer  the 
entire  apparatus  sinks 
below  the  surface  of  the 
same. 


FIG.  41. 


New  York  Testing  Laboratory 
Float  Apparatus. 


"The  time,  in  seconds,  elapsing  between  placing  the  appa- 
ratus on  the  water  and  when  it  sinks,  is  determined  most  con- 


EXAMINATION   OF   BITUMINOUS    ROAD    MATERIALS       341 

veniently  by  means  of  a  stop  watch,  and  is  considered  as  the 
consistency  of  the  bitumen  under  examination." 

(Value  of  test.)  The  author  has  employed  this  test  in  the 
examination  of  a  variety  of  road  binders  and  finds  that,  while 
it  is  an  admirable  means  of  identification,  it  does  not  always 
give  a  true  idea  of  the  relative  consistency  of  different  classes 
of  bitumens.  This  is  only  to  be  expected  when  one  considers  the 
fact  that  different  products  may  vary  greatly  in  their  specific 
heats.  Moreover,  the  presence  of  solid  impurities  such  as  mineral 
matter  and  free  carbon  may  greatly  affect  the  results.  Its 
main  value  would  seem  to  lie  in  its  use  for  control  work.  The 
author  has  had  occasion  to  employ  it  for  this  purpose  with  con- 
siderable success  in  supervising  the  preparation  of  road  tars. 
Thus  if  in  refining  a  given  material  distillation  is  continued  until 
the  residue  shows  a  definite  and  predetermined  value  according 
to  this  test,  it  is  possible  to  turn  out  a  very  uniform  product 
in  other  respects. 

If  the  float  test  is  made  upon  an  oil  product  it  may  also  be 
employed  to  advantage  in  testing  the  residue  obtained  from  the 
volatilization  test  for  the  purpose  of  ascertaining  what  change 
in  consistency  if  any  has  taken  place. 

Penetration  Test.  —  (Method.)  This  test,  as  applied  in  the 
examination  of  asphalts  and  asphaltic  cements  for  use  in  the 
paving  industry,  is  often  of  value  in  determining  the  hardness  of 
semisolid  and  solid  oil  and  asphalt  road  binders.  A  number 
of  machines  have  been  designed  for  this  purpose  but  the  one 
most  generally  adopted  is  known  as  the  Dow  Penetration 
Machine,  shown  in  Fig.  42.  The  construction  of  this  appa- 
ratus and  its  method  of  operation  as  described  by  Dow  are  given 
below : 

"The  object  of  the  penetration  is  to  ascertain  the  softness  of 
asphalt,  etc.,  and  is  accomplished  by  determining  the  distance 
a  weighted  needle  will  penetrate  into  the  specimens  under 
examination. 

"So  that  all  tests  may  be  comparable,  a  standard  needle 
should  be  used,  weighted  with  a  constant  weight.  The  tests 


342 


DUST   PREVENTIVES   AND   ROAD   BINDERS 


should  be  made  on  samples  at  a  standard  temperature  and 
be  made  for  the  same  length  of  time  in  every  case.  The 
standards  used  in  this  machine  for  testing  cements  to  see  that 


A 

^-i  H 


FIG.  42.     Dow  Penetration  Machine. 

they  are  of  uniform  consistency  are  a  No.  2  needle,  weighted 
with  100  grams,  penetrating  for  five  seconds  into  the  sample 
at  a  temperature  of  77°  F.  (25°  C.). 

"The  apparatus  consists  of  a  No.  2  needle  A,  inserted  in  a 
short  brass  rod  which  is  held  in  the  aluminum  rod  C  by  the 
binding  screw  B.  The  aluminum  rod  is  secured  in  a  frame- 
work so  weighted  and  balanced  that  when  it  is  supported  on 
the  point  of  the  needle  A  the  framework  and  rod  will  stand  in 


EXAMINATION    OF   BITUMINOUS    ROAD    MATERIALS       343 

an  upright  position,  allowing  the  needle  to  penetrate  perpen- 
dicularly without  the  aid  of  a  support,  thus  doing  away  with 
any  friction. 

"The  frame,  aluminum  rod,  and  needle  weigh  100  grams 
with  the  weight  on  bottom  of  frame;  without  weight,  50  grams. 
Thus  when  the  point  of  the  needle  rests  on  the  surface  of  the 
sample  of  material  to  be  tested  as  to  the  penetration,  it  will 
penetrate  into  the  sample  under  a  weight  of  100  grams  or  50 
grams  as  desired. 

"The  needle  and  weighted  frame  are  shown  in  Fig.  42,  side 
and  front  views  of  the  entire  apparatus  put  together  and  ready 
for  making  a  penetration.  D  is  the  shelf  for  the  sample,  E 
is  the  clamp  to  hold  the  aluminum  rod  C  until  it  is  desired  to 
make  a  test,  F  is  a  button  which  when  pressed  opens  clamp  E. 
By  turning  this  button  while  the  clamp  is  being  held  open  it  will 
lock  and  keep  the  clamp  from  closing  until  unlocked.  The 
device  to  measure  the  distance  penetrated  by  the  needle  consists 
of  a  rack,  the  foot  of  which  is  G.  The  movement  of  this  rack 
up  or  down  turns  a  pinion  to  which  is  attached  the  hand  which 
indicates  on  dial  K  the  distance  moved  by  the  rack.  One 
division  of  the  dial  corresponds  to  a  movement  of  the  rack  of 

-  cm.     The    rack    can   be    raised    or    lowered    by  moving 

counterweight  H  up  or  down.  L  is  a  tin  box  containing  sample 
to  be  tested  which  is  covered  with  water  in  the  glass  cup,  thus 
keeping  its  temperature  constant.  M'M'  are  leveling  screws. 
A  clock  movement  having  a  ten-inch  pendulum  is  attached  to 
the  wall  to  one  side  of  the  machine.  Make  a  mark  P  on  the 
wall  at  the  extremity  of  the  swing  of  the  pendulum;  a  double 
swing  of  this  pendulum,  that  is,  from  the  time  it  leaves  P  until  it 
returns,  is  one  second. 

"The  only  other  things  necessary  to  complete  the  outfit  are 
a  large  dish  pan,  a  pitcher  to  hold  ice  water  and  a  tin  for  hot 
water;  a  coffeepot  is  a  good  thing. 

"To  make  penetration  tests  place  the  materials  contained  in 
circular  tins,  along  with  the  glass  dish,  under  five  or  six  inches  of 


344  DUST   PREVENTIVES   AND   ROAD   BINDERS 

water  in  the  dish  pan,  which  should  have  been  previously 
brought  to  a  temperature  of  77°  F.  by  the  addition  of  hot  water 
or  cold  water. 

"While  the  samples  are  under  the  water  it  should  be  stirred 
every  few  minutes,  with  the  thermometer  and  the  temperature 
kept  constant  at  77°  F.  by  the  addition  of  hot  or  cold  water  as  the 
case  may  require.  The  samples  should  remain  under  the  water 
for  at  least  fifteen  minutes  and  in  cases  where  they  are  very  cold 
or  hot,  at  least  one-half  hour.  The  most  expeditious  way  to 
proceed  in  testing  a  sample  just  taken  from  a  still  or  tank  is  to 
immerse  it  in  ice  water  as  soon  as  it  has  hardened  sufficiently 
and  keep  it  there  for  ten  minutes,  then  in  the  water  at  77°  F.  and 
keep  it  there  for  fifteen  minutes.  When  the  sample  has  remained 
in  the  water  for  the  specified  time  it  is  ready  to  penetrate. 

"The  aluminum  rod  C  should  be  pressed  up  through  the  clamp 
E  so  that  it  will  be  at  such  a  height  that  the  glass  cup  will  easily 
pass  under  it  when  placed  on  shelf  D. 

"A  sample  in  tin  box  should  now  be  placed  in  the  glass  cup 
and  removed  in  it  covered  with  as  much  water  as  convenient 
without  spilling. 

"The  glass  cup  containing  sample  is  placed  on  shelf  D  under 
C.  Insert  brass  rod  with  needle  into  C  and  secure  by  tighten- 
ing binding  screw  B,  lower  C  until  the  point  of  the  needle  very 
nearly  touches  surface  of  sample;  then,  by  grasping  the  frame 
with  two  hands  at  S  and  S',  cautiously  pull  down  until  needle 
is  just  in  contact  with  surface  of  sample. 

"This  can  best  be  seen  by  having  a  light  so  situated  that, 
looking  through  the  sides  of  the  glass  cup,  the  needle  will  be 
reflected  in  the  surface  of  the  sample.  After  thus  setting  the 
needle,  raise  counterweight  H  slowly  until  the  foot  of  the  rack 
G  rests  on  the  head  of  rod  C;  note  reading  of  dial,  place  thumb 
of  right  hand  on  R  and  press  button  with  forefinger,  thus  open- 
ing the  clamp. 

"Hold  open  for  five  seconds  and  then  allow  it  to  close.  The 
difference  between  the  former  reading  of  the  dial  and  the  presr 
ent  is  the  distance  penetrated  by  the  needle,  or  the  penetra- 


EXAMINATION   OF   BITUMINOUS    ROAD   MATERIALS       345 

tion  of  the  sample.  Raise  rack,  loosen  binding  screw  B,  raise 
rod  through  clamp,  leaving  the  needle  sticking  in  sample. 
Remove  needle  from  sample,  clean  well  by  passing  through  a 
dry  cloth,  replace  needle  in  C  and  the  machine  is  ready  for 
another  test. 

"Do  not  clean  needle  on  oily  cloth,  or  waste. 

"Do  not  allow  rack  to  descend  too  rapidly  on  rod  C  as  it  may 
force  C  through  the  clamp,  thus  spoiling  the  reading. 

"  After  using  the  machine,  leave  it  so  the  top  of  the  rack  is 
just  level  with  its  base.  You  will  thus  prevent  dust  from 
entering  and  getting  into  pinion.  When  not  in  use  keep 
machine  covered  with  a  cloth  to  protect  from  dust. 

"  Examine  point  of  needle  from  time  to  time  with  magni- 
fying glass  to  see  that  it  is  not  injured  in  any  way. 

"If  the  needle  is  found  defective,  remove  by  heating  the 
brass  rod,  when  the  needle  can  be  withdrawn  with  pinchers. 
Break  eye  from  one  of  the  extra  needles  and  press  into  brass 
rod  previously  heated. 

"If  needle  does  not  stay  in  well,  insert  it  with  a  small  lump 
of  asphalt. 

"If  when  this  framework  is  supported  on  the  point  of  the 
needle  it  does  not  balance  so  that  the  aluminum  rod  C  stands 
perfectly  perpendicular,  the  frame  is  bent  and  should  be 
straightened  until  the  rod  stands  perpendicular.  This  can 
easily  be  done  by  hand. 

"If  rack  G  does  not  descend  readily  of  its  own  weight  when 
counter  weight  H  is  raised,  it  is  likely  that  dust  has  gotten 
into  the  pinion.  To  get  at  pinion  to  clean,  remove  dial  K  and 
bearing  T,  when  pinion  can  be  pulled  out  sufficiently  far  to 
clean. 

"Never  oil  rack  and  pinion,  as  it  prevents  a  free  movement 
of  rack. 

"The  standards  that  I  have  adopted  for  this  test  are: 

"The  distance  penetrated  by  the  No.  2  needle  into  the  sample 
at  32°  F.  in  one  minute  with  200  grams  on  frame. 

"The  penetration  at  77°  F.  as  described  before,  and  the  pene- 


346 


DUST  PREVENTIVES   AND    ROAD   BINDERS 


FIG.  43.     New  York  Testing  Laboratory  Penetrometer.     (Portable  size.) 

tration  into  the  sample  of  the  No.  2  needle  in  five  seconds  at 
100°  F.  with  5o-gram  frame.  In  some  cases  I  use  100  grams, 
which  is  preferable  if  the  depth  of  the  sample  will  permit.  In 
all  cases  when  you  give  a  penetration  of  cement  state  in  parenthe- 
ses how  it  was  made,  as,  for  example,  (No.  2  N.,  5  sec.,  50  grams, 
100°)  means  that  the  penetration  was  made  with  a  No.  2  needle 
penetrating  5  seconds  with  5o-gram  frame  at  100°  F. 

"If  a  statement  is  made  like  this  there  can  never  be  any 
doubt  about  the  figures,  and  they  will  be  understood  by  all 
familiar  with  the  machine." 

Another  type  of  machine  using  the  same  standards  and  oper- 
ated in  a  very  similar  manner  is  known  as  the  New  York  Test- 
ing Laboratory  Penetrometer.  This  is  made  in  two  sizes,  a 


EXAMINATION   OF  BITUMINOUS   ROAD    MATERIALS      34^ 

laboratory  and  portable  size.  The  latter  is  shown  in  Fig.  43, 
and  is  described  by  Forrest  *  as  follows : 

"The  diameter  of  the  dial  is  three  inches  and  the  height 
over  all  is  but  eleven  inches.  The  weight  upon  the  needle 
point  is  fixed  at  100  grams  and  the  time  of  penetration  should 
be  taken  by  a  watch.  The  hand  indicating  the  degree  of  pen- 
etration is  adjustable. 

"To  adjust  and  maintain  the  standard  temperature  of  77°  F. 
at  which  the  test  is  made,  the  instrument  and  the  sample  of 
bitumen,  the  latter  in  a  tin  box  one-half  inch  deep  by  two  and 
one-half  inches  diameter,  are  placed  in  a  tub  of  water,  thus 
obviating  the  necessity  of  adjusting  the  temperature  of  the 
room.  A  depth  of  two  and  one-half  inches  of  water  is  suffi- 
cient." 

Whichever  instrument  is  used  the  results  of  tests  should  be 
reported  according  to  the  form  suggested  by  Dow.  For  the 
softer  bituminous  road  binders  it  is  often  desirable  to  make  the 
test  at  25°  C.  with  a  50  gm.  weight,  but  when  possible  the  re- 
sults obtained  from  the  100  gm.  weight  should  also  be  reported. 
It  is  also  advisable  in  many  instances  to  determine  the  pene- 
tration of  the  residue  obtained  from  the  volatilization  test  as 
compared  with  that  of  the  original  material  in  order  to  detect 
any  change  in  consistency  that  has  taken  place  through 
heating. 

(Value  of  test.)  The  penetration  test,  like  the  float  test,  is 
a  convenient  one  to  employ  for  identification  and  control,  and 
is  often  indicative  of  the  value  of  an  oil  or  asphalt  product  for 
construction  work.  While  the  test  for  bituminous  road  materials 
is  made  in  the  same  manner  as  in  asphalt  paving  work,  the  stand- 
ards for  road  purposes  are  somewhat  different.  No  oil  product 
should  be  employed  in  macadam  construction  twith  a  pene- 
tration higher  than  25.0  mm.  when  tested  at  25°  C.  with  a 
No.  2  needle  for  5  seconds  under  a  weight  of  100  gms.,  unless 
it  possesses  the  property  of  hardening  considerably  when  sub- 
jected to  the  volatilization  test.  On  the  other  hand,  it  is  rarely 

*  Proc.  Am.  Soc.  for  Test.  Mat.,  1909,  Vol.  IX,  p.  600. 


348  DUST   PREVENTIVES   AND   ROAD   BINDERS 


necessary  to  require  a  penetration  as  high  ?  as  that  for  asphaltic 
cement  used  in  the  topping  of  an  asphalt  pavement,  for  the 
reason  that  the  upper  course  of  a  macadam  has  much  greater 
inherent  stability  than  the  sand  course  of  the  asphalt  pave- 
ment. A  penetration  of  from  10.0  to  15.0  mm.  is  usually  con- 
sidered sufficient  for  road  work.  If  a  material  having  a  much 
lower  penetration  is  selected,  its  susceptibility  to  temperature 
changes  will  have  to  be  considered.  Blown  oils  being  but 
little  affected  by  temperature  changes  may  run  as  low  as  4.0  mm. 
with  little  danger  of  becoming  too  hard  in  cold  weather.  They 
are,  however,  less  ductile  than  the  oil  pitches  and  asphaltic 
cements  of  like  consistency  and  somewhat  less  desirable  for 
road  work  on  this  account.  The  significance  of  the  penetra- 
tion determination  made  upon  residues  obtained  from  the 
volatilization  test  will  be  discussed  under  the  latter.  Pene- 
tration determinations  are  seldom  made  upon  tars,  because 
their  surface  tension  is  so  high  that  even  approximately  cor- 
rect penetrations  cannot  be  recorded  and  the  presence  of  free 
carbon  in  varying  quantities  seriously  affects  the  results. 

Ductility  Test.  —  A  test  for  ductility  has  been  employed  to 
some  extent  in  the  examination  of  asphaltic  cements  to  be  used 
in  the  paving  industry.  It  is  mentioned  here  only  because  a 
tendency  has  been  exhibited  to  make  use  of  it  in  connection 
with  the  examination  of  road  binders,  and  it  is  difficult  to  see 
how  it  can  be  of  any  great  value  for  this  purpose.  Road 
binders  vary  so  greatly  in  consistency  that  in  order  to  sub- 
ject them  to  the  test  and  make  it  a  comparative  one,  the  ma- 
terial should  be  brought  to  a  definite  point  of  consistency  as 
determined  by  the  penetration  method.  This  can  be  accomp- 
lished by  heating  it  until  sufficient  volatile  matter  has  been 
driven  off  to  produce  a  residue  of  the  desired  consistency. 
This  method  will,  however,  often  prove  to  be  a  long  and  tedi- 
ous operation,  and  in  the  case  of  many  asphaltic  oils  results  in 
a  chemical  alteration  due  to  the  application  of  high  tempera- 
tures, which  produces  a  residue  quite  unlike  any  residue  which 
would  be  formed  under  ordinary  service  conditions.  Being  an 


EXAMINATION   OF   BITUMINOUS    ROAD    MATERIALS       349 


entirely  different  product,  its  ductility  can  in  no  way  be  con- 
sidered a  measure  of  that  of  the  original  material. 

Such  a  test  may,  however,  prove  of  some  value  if  made  upon 
the  harder  types  of  bituminous  road  materials  or  the  residues 
obtained  from  the  volatilization  test  described  later  in  this 
chapte'r.  For  a  full  description  of  the  ductility  test  reference 
should  be  made  to  a  recent  paper  by  Smith.* 

Melting  Point.  —  (Method.)  Bitumens  being  mixtures  of 
various  organic  compounds  can  have  no  true  melting  point,  but 
an  arbitrary  method  for  determining  the  so-called  melting  point 
of  those  materials  sufficiently  solid  to  maintain  their  form  for 
some  time  under  normal  conditions,  is  of  value  as  a  means  of 
identification  and  for  control  work.  The  author  has  tried  a 
number  of  methods  and 
has  selected  the  following 
as  being  most  convenient 
and  accurate  for  such 
work. 

The  material  under  ex- 
amination is  first  melted 
by  the  gentle  application 
of  heat  until  sufficiently 
fluid  to  pour  readily,  care 
being  taken  that  it  suffers 
no  appreciable  loss  by 

volatilization.  It  is  then  FIG.  44.  Brass  Cubical  Mold.  (Double.) 
poured  into  a  one-half 

inch  brass  cubical  mold  which  has  been  amalgamated  with 
mercury  and  which  is  placed  on  an  amalgamated  brass  plate 
as  shown  in  Fig.  44.  The  brass  may  be  amalgamated  by  wash- 
ing it  first  in  dilute  hydrochloric  acid,  after  which  the  mercury 
is  rubbed  into  the  surface.  By  this  means  the  bitumen  is  to 
a  considerable  extent  prevented  from  sticking  to  the  sides  of 
the  mold. 


*  "  A  Machine  Testing  the  Ductility  of  Bituminous  Paving  Cements."     Proc. 
Am.  Soc.  for  Test.  Mat.,  1909,  Vol.  IX,  p.  594. 


350  DUST   PREVENTIVES   AND    ROAD   BINDERS 

After  cooling,  the  cube  is  removed  from  the  mold  and  fastened 
upon  the  lower  arm  of  a  No.  12  B  &  S.  wire,  bent  at  right  angles 
and  suspended  beside  a  thermometer  in  a  covered  Jena  glass 
beaker  of  400  cc.  capacity,  which  is  placed  in  a  water  or  sul- 
phuric acid  bath.  The  wire  should  be  passed  through  the 
center  of  two  opposite  faces  of  the  cube,  which  is  suspended  one 
inch  above  the  bottom  of  the  beaker.  This  piece  of  apparatus  is 
shown  in  Fig.  45.  The  water  or  acid  bath  consists  of  an  800  cc. 
low  form  Jena  glass  beaker  suitably  mounted  for  the  applica- 
tion of  heat  from  below.  The  beaker  in  which  the  cube  is 
suspended  is  of  the  tall  form  Jena  type  without  lip.  The  metal 
cover  has  two  openings.  A  cork,  through  which  passes  the 
upper  arm  of  the  wire,  is  inserted  in  one  and  the  thermometer  in 
the  other.  The  bulb  of  the  thermometer  should  be  just  level 
with  the  cube  and  at  an  equal  distance  from  the  side  of  the 
beaker.  In  order  that  a  reading  of  the  thermometer  may  be 
made  if  necessary  at  the  point  where  it  passes  through  the  cover, 
the  hole  is  shaped  as  shown  in  the  smaller  illustration  and 
covered  with  an  ordinary  object  glass  through  which  the  stem 
of  the  thermometer  may  be  seen.  Readings  made  through  this 
glass  should  be  calibrated  to  the  angle  of  observation,  which 
may  be  made  constant  by  always  sighting  from  the  front  edge 
of  the  opening  to  any  given  point  on  the  stem  of  the  thermometer 
below  the  cover. 

After  the  test  specimen  has  been  placed  in  the  apparatus  the 
liquid  in  the  outer  vessel  is  heated  in  such  a  manner  that  the 
thermometer  registers  an  increase  of  5°  C.  per  minute.  The  tem- 
perature at  which  the  bitumen  touches  a  piece  of  paper  placed 
in  the  bottom  of  the  beaker  is  taken  as  the  melting  point. 
Determinations  made  in  the  manner  above  described  should  not 
vary  more  than  two  degrees  for  different  tests  of  the  same 
material.  At  the  beginning  of  this  test  the  temperature  of  both 
bitumen  and  bath  should  be  approximately  25°  C. 

(Value  of  test.)  This  test  can  of  course  be  made  only  on 
materials  intended  for  road  construction.  The  melting  point 
of  a  bitumen  is  directly  related  to  its  hardness  and  brittleness, 


EXAMINATION    OF   BITUMINOUS    ROAD    MATERIALS        351 


352  DUST   PREVENTIVES   AND    ROAD    BINDERS 

but  the  relations  are  not  the  same  for  all  classes.  Thus,  at 
normal  temperature  a  blown  oil  with  a  melting  point  of  50°  C. 
is  neither  hard  nor  brittle,  while  a  tar  pitch  is  both.  As  the 
melting  point  rises,  however,  they  both  become  harder  and 
more  brittle.  For  road  work,  the  melting  point  of  a  tar  pitch 
should  rarely  exceed  40°  C.,  while  that  of  a  blown  product  may 
run  as  high  as  65°  C.  and  over,  without  fear  of  the  material 
cracking  in  cold  weather.  Oil  pitches  and  the  asphaltic  cements 
hold  an  intermediate  position  between  these  two.  The  climate 
under  which  a  bitumen  is  to  serve  as  a  road  binder  could  be 
considered  in  connection  with  its  melting  point,  and  this  is  par- 
ticularly true  of  tar  products.  Thus  in  a  cold  climate,  where 
the  winters  are  severe,  it  is  preferable  to  employ  a  tar  pitch 
having  a  melting  point  much  lower  than  40°  C.;  in  fact,  under 
very  severe  conditions,  one  that  will  melt  as  low  as  20°  C. 

The  desired  method  of  application  will  also  have  to  be  taken 
into  account.  If  the  penetration  or  grouting  method  is  to  be 
followed,  the  melting  point  of  a  tar  product  should  not  exceed 
25°  C.,  and  in  a  blown  oil  probably  not  over  30°  to  35°  C.,  for 
the  reason  that  if  higher  than  this  the  material  is  apt  to  solidify 
too  quickly  upon  coming  in  contact  with  the  cold  stone  on  the 
road,  and  will,  therefore,  not  penetrate  to  any  extent.  When  the 
mixing  method  is  to  be  employed  using  hot  stone,  the  melting 
point  of  the  bitumen  may  be  as  high  as  climatic  conditions  will 
allow.  Oil  products  for  application  in  earth  road  construction 
should  have  a  melting  point  considerably  below  normal  tempera- 
ture or  otherwise  it  will  be  extremely  difficult  to  mix  them  with 
the  cold  earth.  If  the  earth  can  be  heated,  however,  and 
mixed  with  the  oil  before  application  to  the  road,  a  product 
having  a  higher  melting  point  is  to  be  preferred. 

Volatilization.  —  (Method.)  This  test  is  made  in  a  manner 
quite  similar  to  the  method  described  by  Richardson*  for 
examining  refined  asphalts.  Twenty  grams  of  the  material 
to  be  tested  is  placed  in  a  circular  tin  dish  about  six  cm.  in 
diameter  and  two  cm.  deep  which  has  previously  been  weighed. 

*  The  Modern  Asphalt  Pavement,  loc.  cit. 


EXAMINATION   OF   BITUMINOUS   ROAD   MATERIALS       353 

It  is  then  heated  in  an  oven  for  five  hours  at  a  constant  tem- 
perature of  163°  C.  and  after  cooling  the  percentage  loss  in 
weight  determined.  The  oven  should  be  so  designed  that  an 
even  temperature  may  be  maintained,  and  a  thermostat  or 
other  mechanical  device  should  be  employed  to  keep  the 
temperature  constant.  Two  thermometers  are  required,  one 
to  show  the  temperature  of  the  air  in  the  oven  and  the  other 
immersed  in  a  non-volatile  oil  to  show  the  temperature  of  the 
material  tested.  The  former  is  of  use  for  determining  rapid 
changes  of  temperature,  so  that  the  supply  of  heat  can  be 
quickly  regulated.  The  temperature  of  the  latter  is,  however, 
the  one  which  should  govern  the  final  regulation. 

It  is  important  that  the  containing  vessels  be  of  uniform 
dimensions  in  this  test  in  order  to  obtain  comparative  results. 
When  carefully  made  such  determinations  are  accurate  to 
within  about  0.5  of  i%,  provided  the  total  percentage  of  vola- 
tile matter  is  not  extremely  high. 

(Interpretation  of  results.)  That  this  is  not  a  quantitative 
determination  of  any  one  class  of  volatile  oils  which  may  be 
present  in  the  original  material  can  be  seen  in  the  table  follow- 
ing. These  results  were  obtained  by  determining  the  loss  in 
weight  of  two  different  oils,  fresh  samples  of  which  were  then 
mixed  in  the  given  proportions  and  the  loss  determined  for  the 
mixtures.  It  will  be  noticed  that  the  presence  of  the  less  vol- 
atile oil  retarded  the  volatilization  of  the  mixture  to  a  con- 
siderable extent.  It  would  not  therefore  seem  advisable  to 
designate  these  volatile  materials  as  a  class  which  may  be 
separated  by  this  means,  but  to  simply  report  the  results  as 
loss  upon  heating  at  the  given  temperature  for  a  given  length 
of  time. 

VOLATILIZATION   TEST   OF    OIL   MIXTURES. 


Oil  No. 

Character. 

Loss. 

i 

Petroleum  distillate 

T3  J3% 

12    87% 

Petroleum  residue 

0.18% 

0.16% 

7 

20  per  cent  No    2,  80  per  cent  No    i           ... 

8.4?% 

8.07% 

Calculated  

10.45% 

V 

354  DUST   PREVENTIVES   AND   ROAD   BINDERS 

Some  analysts  make  this  test  upon  50  grams  of  the  material 
instead  of  20  grams.  When  this  is  done  either  a  container  which 
will  expose  a  proportionately  greater  surface  should  be  em- 
ployed or  else  the  time  of  the  test  should  be  considerably 
lengthened  in  order  to  obtain  results  at  all  comparable  with  the 
method  described  above. 

While  the  volatilization  test  is  a  purely  arbitrary  one,  when 
applied  to  road  oils  and  asphaltic  preparations,  it  will  often  prove 
of  considerable  value.  Applied  to  tars  it  is  of  less  value  because 
of  misleading  results  produced  by  the  retaining  effect,  noted  on 
page  262,  of  the  free  carbon  upon  the  volatile  oils.  As  applied  to 
oil  and  asphalt  compounds  it  is  believed  that  the  loss  in  weight 
thus  produced  is  a  fair  comparative  indication  of  loss  by  volatiliza- 
tion suffered  by  the  material  in  the  course  of  time  when  applied 
to  the  road,  also  that  the  character  of  the  residue  is  similar  to 
that  eventually  left  in  the  road.  A  determination  of  the  con- 
sistency of  this  residue  should  if  possible  be  made,  and  particu- 
lar attention  paid  as  to  whether  it  is  of  a  greasy  or  sticky  nature. 
The  volatilization  test  is  not  a  quantitative  determination  of 
any  one  class  of  volatile  oils  present  in  the  original  material,  but 
only  of  its  tendency  to  give  up  these  volatile  oils.  If  the  material 
has  a  certain  consistency  which  it  is  desired  to  maintain  after 
application,  it  should  show  a  low  volatilization  and  should  not 
be  subject  to  hardening  by  oxidation  or  other  causes.  A  deter- 
mination of  penetration  of  the  residue  as  compared  with  that 
of  the  original  material  is  of  value  in  determining  this  fact.  A 
material  which  must  be  soft  and  sometimes  fluid  on  account  of 
the  desired  method  of  application  and  character  of  the  road 
treated  should  very  properly  suffer  high  loss  by  volatiliza- 
tion in  order  that  it  may  be  capable  of  attaining  proper  con- 
sistency under  service  conditions.  This  is  particularly  true 
of  oils  that  are  to  be  applied  during  the  construction  of 
oiled  earth  roads,  in  which  case  a  loss  of  from  20  to  30  per 
cent  is  not  uncommon.  Fluid  products  that  will  not  volatilize 
to  any  extent  nor  harden  under  this  test  are  unfit  for  any  sort 
of  construction  work  and  their  use  for  this  purpose  can  only 


EXAMINATION   OF   BITUMINOUS    ROAD    MATERIALS        355 

result  in  failure.  The  great  bulk  of  residual  oils  belongs  to  this 
class  of  materials.  If  the  residue  shows  a  penetration  of  over 
25.0  mm.  the  material  will  never  prove  satisfactory,  except  in 
roads  subjected  to  very  light  traffic.  As  a  rule,  it  may  be  said 
that  other  things  being  equal,  the  suitability  of  an  oil  for  use 
in  the  construction  of  roads  increases  as  the  penetration  of  its 
residue  decreases.  An  oil  showing  a  penetration  of  from  10.0 
to  15.0  mm.  should  suffer  but  little  loss  by  volatilization,  usually 
less  than  one  per  cent,  and  the  penetration  of  its  residue  should 
not  be  greatly  lowered. 

Fluid  products  to  be  used  in  the  surface  treatment  of  roads 
need  not  necessarily  show  a  high  loss  by  volatilization  nor  a 
great  increase  in  the  consistency  of  their  residues,  although  the 
latter  is  a  desirable  property.  They  are  mainly  of  value  as 
dust  preventives  and  binders  for  the  thin  coat  of  fine  material 
upon  the  road  surface  and  cannot  affect  the  character  of  the 
road  proper  unless  applied  in  large  quantities.  If  their  resi- 
dues are  not  of  a  sticky  nature,  they  will,  however,  produce 
an  undesirable  surface  condition  in  wet  weather  unless  applied 
in  very  small  quantities.  In  general  all  residues  should  be 
sticky  or  adhesive,  as  otherwise  they  will  act  more  as  lubricants 
than  as  road  binders.  A  paraffin  oil  will  produce  a  greasy 
residue,  while  an  asphaltic  oil  will  produce  one  that  has  con- 
siderable binding  value.  It  is  for  this  reason  that  the  latter 
may  be  successfully  employed  in  road  work,  while  the  former 
are  worthless  for  this  purpose. 

In  certain  instances,  determinations  of  the  so-called  asphalt 
contents  of  oils  have  been  made  by  driving  off  volatiles  until 
the  residue  is  of  a  certain  consistency.  To  produce  this  resi- 
due it  is  often  necessary  to  subject  the  bitumen  to  such  high 
temperatures  that  chemical  changes  take  place  which  would 
never  occur  under  service  conditions.  For  this  reason  the  test 
is  not  a  determination  of  the  actual  asphalt  contents,  but  only 
of  the  ability  of  the  oil  to  produce  an  asphaltic  base  of  given 
consistency  under  the  action  of  high  temperatures.  Such  a 
test  is,  therefore,  misleading  and  has  resulted  in  much  con- 


DUST   PREVENTIVES    AND    ROAD   BINDERS 

fusion  among  road  engineers  as  to  the  relative  binding  value  of 
oils.  This  matter  has  been  discussed  to  some  extent  by  the 
author  elsewhere  in  this  book. 

Besides  the  temperature  of  163°  C.  it  may  in  some  instances 
be  advisable  to  determine  the  volatilization  of  a  material  at 
100°  C.  or  even  lower  in  order  to  ascertain  whether  or  not  it 
is  capable  of  rapidly  increasing  in  consistency  under  service 
conditions.  In  such  cases  the  same  general  method  is  followed 
as  described  for  the  higher  temperature. 

Total  Bitumen.  —(Method.)  For  practical  purposes,  all 
organic  matter  soluble  in  carbon  bisulphide  (or  carbon  disul- 
phide,  as  it  is  often  called)  is  considered  as  bitumen  in  this 
determination  and  the  total  bitumen  found  by  digesting  the 
material  to  be  examined  in  this  solvent  and  filtering  off  the 
insoluble  residue.  The  method  which  the  author  employs  is 
practically  identical  with  the  "  Rapid  Method  for  the  Deter- 
mination of  Material  in  Bituminous  Road  Compounds  Insol- 
uble in  Cold  Carbon  Bisulphide"  suggested  by  the  American 
Society  for  Testing  Materials.  From  one  to  ten  grams  of 
the  water-free  material  (depending  upon  the  amount  of  bi- 
tumen present)  are  weighed  into  a  150  cc.  Erlenmeyer  flask, 
the  tare  of  which  has  been  previously  ascertained,  and  treated 
with  1 60  cc.  of  c.p.  carbon  bisulphide.  The  flask  is  then  loosely 
corked  and  shaken  from  time  to  time  until  practically  all  large 
particles  of  the  material  have  been  broken  up,  when  it  is  set 
aside  for  not  less  than  fifteen  hours.  At  the  end  of  this  time 
the  contents  of  the  flask  are  decanted  off  upon  a  weighed 
Gooch  crucible  fitted  with  a  long-fiber  amphibole  asbestos 
filter.  The  residue  remaining  in  the  flask  is  then  washed  with 
50  cc.  of  carbon  disulphide,  allowed  to  settle,  and  decanted  as 
before,  the  insoluble  matter  being  finally  brought  upon  the  filter 
and  washed  with  100  cc.  carbon  disulphide,  or  until  the  washings 
are  practically  colorless.  The  filter  and  contents  are  then  dried 
at  125°  C.,  cooled  and  weighed.  Should  any  residue  remain  in 
the  flask,  it  is  also  dried  and  weighed  and  this  weight  added  to 
that  of  the  residue  in  the  crucible.  Where  great  accuracy  is 


EXAMINATION   OF  BITUMINOUS   ROAD   MATERIALS       357 


desired,  the  filtrate  should  be  burned  off  and  ignited  to  an  ash  and 
the  weight  of  the  ash  thus  obtained  added  to  that  of  the  insoluble 
residue.  The  weight 
of  the  total  residue 
deducted  from  that  of 
the  original  material 
gives  the  weight  of  bi- 
tumen soluble  in  cold 
carbon  disulphide.  In 
case  of  tars  and  pitches 
the  percentage  of  in- 
soluble residue,  deter- 
mined as  above,  minus 
that  of  any  ash  which 
may  be  found  by  igni- 
tion, is  reported  as  free 
carbon.  In  oils  it  is 
reported  as  organic 
matter  insoluble. 

The  form  of  Gooch 
crucible  best  adapted 
for  such  determina- 
tions holds  30  cc.,  is 
4.4  cm.  wide  at  the  top, 
tapering  to  3.6  cm. 
at  the  bottom,  and 
2.6  cm.  deep.  The  felt 
is  made  by  beating  up 
the  asbestos  in  a  mor- 
tar and  suspending 
the  finer  particles  in 
water.  It  is  well  to 
have  a  stock  bottle 
of  this  mixture  always 
on  hand.  The  suspended  asbestos  is  poured  into  the  crucible, 
which  has  in  the  meantime  been  placed  in  the  vacuum  filtering 


FIG.  46.     Filtering  Apparatus  for  the  Deter- 
mination of  Total  Bitumen. 


358  DUST   PREVENTIVES   AND    ROAD    BINDERS 

flask  as  shown  in  Fig.  46.  As  soon  as  the  asbestos  has  some- 
what settled  vacuum  is  applied  and  the  felt  deposited  on  the 
bottom  of  the  crucible,  which  is  then  dried,  ignited,  cooled  in  a 
desiccator  and  weighed.  The  prepared  felt  should  be  dense 
enough  to  just  barely  transmit  light  when  held  so  that  the  bottom 
of  the  crucible  is  between  the  eye  and  the  source  of  light.  If 
it  is  denser  than  this  the  filter  is  apt  to  clog,  and  if  much  thinner 
to  let  through  the  finer  particles  of  insoluble  material.  With 
a  little  practice  it  is  possible  to  prepare  a  uniform  felt  without 
difficulty.  In  the  carbon  bisulphide  extraction  it  is  seldom 
necessary  to  make  use  of  the  vacuum  during  filtration,  but  it 
is  convenient  to  filter  into  the  vacuum  flask,  in  which  case 
vacuum  may  be  applied  if  desired.  The  carbon  bisulphide 
for  this  determination  should  be  chemically  pure  and  when 
shaken  with  a  little  clean  mercury  should  show  no  discolora- 
tion of  the  latter. 

As  applied  to  asphalts  Richardson  *  has  shown  that  finely 
divided  inorganic  material  when  present  retains  a  certain 
amount  of  bitumen  which  cannot  be  removed  by  carbon  di- 
sulphide,  and  this  is  undoubtedly  true  of  some  road  binders. 
Free  carbon  as  found  in  tar  probably  exhibits  a  similar  absorb- 
ent action.  For  all  practical  purposes,  however,  this  defect  in 
the  method  may  be  neglected.  Various  forms  of  extraction 
apparatus  are  sometimes  employed  for  this  determination,  but 
the  method  described  has  been  found  most  suitable  for  all 
types  of  bituminous  road  materials. 

(Value  of  test.)  Fluid  oils  are  almost  completely  soluble  in 
carbon  disulphide,  and  also  blown  oils  and  oil  pitches  unless 
they  have  been  cracked  to  the  point  of  producing  free  carbon. 
The  solid  native  bitumens,  with  a  few  exceptions,  are  not  so 
soluble,  as  they  contain  more  or  less  mineral  matter,  together 
with  organic  matter  of  a  non-bituminous  nature.  Thus,  petro- 
leums and  petroleum  products  are  almost  always  soluble  to  the 
extent  of  at  least  99.5  per  cent,  and  should  contain  less  than 
0.2  per  cent  mineral  matter,  while  the  native  asphalts  may  show 

*  Proc.  Am.  Soc.  Test.  Mat.,  1906,  Vol.  VI.,  p.  509. 


EXAMINATION   OF   BITUMINOUS    ROAD    MATERIALS       359 

as  low  as  54  to  56  per  cent  bitumen.  This  is  characteristic 
of  Trinidad  asphalt,  an  average  sample  of  which  will  contain 
approximately  56  per  cent  soluble  in  carbon  bisulphide,  7  per 
cent  organic  matter  insoluble  and  37  per  cent  mineral  matter. 
Bermudez  asphalt  will  show  in  the  neighborhood  of  95  per 
cent  soluble  in  carbon  bisulphide,  and  2.5  per  cent  each  of 
organic  matter  insoluble  and  mineral  matter.  Gilsonite  will 
more  nearly  coincide  with  the  oils  in  this  test,  being  an  ex- 
tremely pure  solid  native  bitumen  soluble  in  carbon  bisulphide 
to  the  extent  of  from  99.4  to  99.6  per  cent.  The  solubility  of 
the  bitumen  itself  is  entirely  independent  of  its  character  and 
consistency,  so  that  the  amount  and  character  of  insoluble 
material  is  of  most  interest  in  this  test.  This  material  is  of 
no  value  from  the  standpoint  of  road  work,  but  indicates 
whether  an  asphalt  has  been  employed  in  the  preparation  of  the 
binder,  also  whether  a  product  has  been  destructively  distilled 
during  its  preparation,  the  determining  factor  in  the  former 
case  being  the  amount  of  mineral  matter  present  and  the 
amount  of  organic  material  in  the  absence  of  mineral  matter 
in  the  latter  case.  It  is  of  course  possible  to  adulterate  a 
preparation  so  as  to  give  misleading  results,  unless  the  ana- 
lyst is  familiar  with  the  characteristics  which  the  addition  of 
various  solid  native  bitumens  will  produce  in  oils  of  different 
types. 

Tars,  with  the  exception  of  those  produced  in  blast  furnaces, 
contain  only  a  small  fraction  of  one  per  cent  mineral  matter. 
Practically  all  material  insoluble  in  carbon  bisulphide  is,  there- 
fore, organic  material,  commonly  known  as  free  carbon.  The 
relation  of  free  carbon  to  the  density  of  tars  has  already  been 
discussed  under  the  specific  gravity  determination,  which,  as 
has  been  shown,  if  taken  in  connection  with  the  consistency 
of  the  tar,  gives  a  good  indication  of  the  percentage  of  this 
constituent. 

Any  tar  or  tar  product  containing  less  than  4  per  cent  free 
carbon  may  almost,  without  exception,  be  considered  as  origi- 
nating in  the  manufacture  of  carburetted  water  gas  and  is 


360  DUST   PREVENTIVES   AND    ROAD    BINDERS 

the  product  of  the  destructive  distillation  of  oil.  Water  gas 
tars  or  oil  tars  will  usually  contain  less  than  this  amount,  even 
when  refined  to  a  specific  gravity  of  1.17,  and  crude  water  gas 
tar  seldom  exceeds  2  per  cent  free  carbon.  Most  crude  coke 
oven  tars  will  carry  from  4  to  10  per  cent  free  carbon,  unless 
they  have  been  produced  at  very  high  temperatures,  while  the 
modern  gas  house  coal  tars  rarely  show  less  than  15  per  cent 
and  sometimes  run  as  high  as  30  per  cent  and  over. 

The  effect  of  free  carbon  in  tars  from  the  standpoint  of  road 
treatment  has  been  fully  discussed  in  Chapter  XI. 

Free  Carbon.  —  This  determination  as  applied  to  tars  is 
described  under  the  total  bitumen  determination.  Some  ana- 
lysts use  benzol  as  a  solvent  in  place  of  carbon  bisulphide, 
and  employ  an  extraction  apparatus.  As  a  rule  the  results 
obtained  with  both  solvents  are  sufficiently  close  to  make  little 
practical  difference,  but  it  is  always  well  when  reporting  this 
constituent  to  state  the  solvent  used  and  the  method  of  deter- 
mination, that  is,  whether  the  Gooch  crucible  or  extractor  has 
been  employed.  In  this  book  free  carbon  should  be  under- 
stood as  material  insoluble  in  carbon  disulphide  according  to 
the  Gooch  method. 

Bitumen  Insoluble  in  86°  B.  Paraffin  Naphtha.  —  (Method.) 
This  determination  is  made  in  the  same  manner  as  the  total 
bitumen  determination  except  .that  86°  Baume  naphtha  is  em- 
ployed as  a  solvent  in  place  of  carbon  disulphide.  The  test 
is  made  only  upon  oil  and  asphalt  products  and  the  per  cent  of 
bitumen  insoluble  is  reported  upon  the  basis  of  total  bitumen 
taken  as  100.  The  difference  between  the  material  insoluble  in 
carbon  disulphide  and  in  the  naphtha  is  the  bitumen  insoluble 
in  the  latter.  Thus  if  in  a  certain  instance  it  is  found  that  the 
material  insoluble  in  carbon  disulphide  amounts  to  i.o  per  cent 
and  that  10.9  per  cent  is  insoluble  in  naphtha,  the  per  cent  of 
bitumen  insoluble  would  be  calculated  as  follows' 

bitumen  insoluble  in  naphtha       10.0  —  i       9.9 

,  .  u.,  -  =  -      =  -  -  =  10  per  cent. 

total  bitumem  100  —  i        99 


EXAMINATION    OF   BITUMINOUS   ROAD   MATERIALS       361 

The  great  objection  to  this  determination  is  that  petroleum 
naphthas  are  by  no  means  definite  compounds,  being  composed 
of  a  number  of  hydrocarbons  which  vary  in  character  and 
quantity  according  to  the  petroleum  from  which  they  have 
been  distilled.  Their  solvent  powers  also  vary  greatly.  Thus 
naphthas  produced  from  asphaltic  petroleums,  consisting  mainly 
of  naphthene  and  polymethylene  hydrocarbons,  are  much  more 
powerful  solvents  of  the  heavier  asphaltic  hydrocarbons  than 
are  the  paraffin  naphthas.  The  density  of  the  naphtha  also 
affects  its  solvent  power,  those  of  high  gravity  dissolving  the 
heavier  hydrocarbons  more  readily  than  those  of  lower  gravity. 
As  the  main  object  of  this  test  is  to  separate  the  heavier  hydro- 
carbons of  an  asphaltic  nature  from  the  paraffin  hydrocarbons, 
a  paraffin  solvent  should  be  employed  and  for  ordinary  pur- 
poses the  author  has  found  a  paraffin  naphtha  of  86°  Baume 
gravity,  boiling  between  40°  and  50°  C.,  to  be  readily  obtainable 
and  fairly  satisfactory.  The  solvent  action  of  88°  naphtha 
is  a  little  lower  and,  therefore,  preferable,  but  it  cannot  be  as 
readily  obtained.  The  use  of  a  definite  paraffin  compound  such 
as  pentane  or  hexane  has  been  suggested  for  this  determination, 
but  these  products  are  very  expensive  and  although  they  would 
be  preferable  to  naphtha  in  many  respects,  until  some  method 
is  devised  by  which  they  may  be  completely  recovered  so  as  to 
be  available  for  repeated  use,  they  are  unlikely  to  be  gener- 
ally adopted.  It  is  difficult  to  employ  an  extractor  for  this 
determination,  owing  to  the  clogging  of  the  filter,  which 
frequently  necessitates  the  use  of  a  vacuum.  When  vacuum 
is  employed  the  loss  of  the  solvent  by  volatilization  is  very 
appreciable. 

(Value  of  the  test.)  The  term  asphaltenes  is  commonly 
applied  to  bitumen  insoluble  in  petroleum  naphtha,  and  mal- 
thenes  to  that  portion  which  is  soluble.  It  is  of  course  evident 
that  both  of  these  terms  cover  a  multitude  of  compounds,  but 
in  general  it  may  be  said  that  the  asphaltenes  tend  to  give  body 
and  consistency  as  well  as  adhesive  properties  to  the  products 
in  which  they  are  found,  so  that  this  determination  serves  as  an 


362  DUST   PREVENTIVES   AND    ROAD    BINDERS 

indication  of  the  mechanical  stability  of  the  material  as  well  as 
its  binding  qualities. 

No  oils  carrying  less  than  4  per  cent  naphtha  insoluble  bitumen 
will  prove  of  service  other  than  as  dust  preventives.  Crude 
paraffin  oils  are  almost  entirely  dissolved  by  this  solvent, 
while  the  asphaltic  oils  contain  very  appreciable  amounts  of 
naphtha  insoluble  bitumen.  Residual  oils  carry  larger  quantities 
than  the  crude  oils  from  which  they  are  produced,  and  blown 
oils,  in  particular,  show  very  high  percentages  of  insoluble 
hydrocarbons,  sometimes  running  as  high  as  25  to  30  per  cent. 
In  this  type  of  oil  the  naphtha  insoluble  bitumen  increases  with 
the  amount  of  blowing  to  which  the  oil  has  been  subjected,  as 
shown  by  the  following  results  taken  from  a  patent  by  Culmer 
and  Culmer:* 

EFFECT    OF    BLOWING    OILS. 

Hours  Blowing.  Per  cent  Asphaltenes. 

0 2.50% 

16 8.03% 

32 23.46% 

40 25 . 14% 

The  solid  native  bitumens  also  run  high  in  this  respect, 
Trinidad  and  Bermudez  asphalt  showing  35  to  40  per  cent 
insoluble  bitumen,  and  gilsonite  as  high  as  45  per  cent.  As- 
phaltic cements  containing  appreciable  quantities  of  these  solid 
products  will  necessarily  show  relatively  high  percentages  of 
bitumen  insoluble  in  naphtha.  While  the  binding  value  of 
asphaltic  oils  and  cements  is  undoubtedly  dependent  upon  the 
presence  of  the  naphtha  insoluble  hydrocarbons,  variations  in  the 
character  of  these  hydrocarbons  exert  a  marked  influence  upon 
the  characteristics  of  the  original  material.  This  matter  has  at 
present  received  but  little  attention  and  just  what  such  differ- 
ences are  and  what  effect  they  have  is  a  matter  for  future  study. 
The  character  of  the  naphtha  soluble  bitumen  after  the  solvent 
has  been  evaporated  is  of  interest  from  the  standpoint  of  road 
treatment,  that  which  is  sticky  after  the  solvent  has  been 
evaporated  indicating  better  road  building  qualities  in  the 
original  material  than  that  which  is  greasy. 

*  U.  S.  Patent  No.  635,430. 


EXAMINATION    OF   BITUMINOUS    ROAD   MATERIALS        363 

Determination  of  Bitumen  Insoluble  in  Carbon  Tetrachloride. 
—  This  determination  is  made  in  exactly  the  same  manner  as 
described  for  the  total  bitumen  determination,  except  that 
carbon  tetrachloride  is  employed  as  a  solvent.  As  in  the  case 
of  the  naphtha  insoluble  bitumen,  the  results  are  calculated  upon 
the  basis  of  the  total  bitumen  present.  Unless  an  oil  has  been 
badly  cracked  or  a  solid  bitumen  such  as  grahamite  added,  this 
determination  is  not  usually  necessary,  as  the  difference  between 
it  and  the  total  bitumen  determination  will  be  negligible.  Only 
when  the  per  cent  of  hydrocarbons  insoluble  in  86°  naphtha  is 
found  to  be  high  should  it  be  employed.  The  bitumens  insoluble 
in  carbon  tetrachloride  have  been  termed  carbenes,  and  in  some 
instances  have  been  included  in  asphalt  specifications.  But 
little  is  known  of  their  effect  upon  the  physical  properties  of 
the  oils  and  asphalts  in  which  they  are  found,  but  as  has  been 
shown  by  Kirschbaum,*  they  are  "the  result  of  unnecessarily 
high  temperatures  and  resulting  concentration  in  the  production 
or  refinement  of  large  quantities  of  both  natural  and  oil  as- 
phalts." It  is  therefore  a  matter  of  interest  to  note  any  con- 
siderable amount  of  these  products  in  oils  which  are  to  be 
used  as  road  binders,  for  the  purpose  of  determining  their  effect 
upon  the  practical  results  obtained.  Most  road  oils  will  be 
found  to  be  equally  soluble  in  carbon  tetrachloride  and  carbon 
disulphide.  While  the  solid  native  bitumens  all  show  a  cer- 
tain percentage  of  carbenes,  grahamite  runs  particularly  high  in 
this  class  of  hydrocarbons.  Carbenes  may,  therefore,  be 
expected  to  occur  in  appreciable  amounts  in  road  binders  pre- 
pared from  this  material. 

Fixed  Carbon.  —  (Method.)  This  determination  is  made  in 
accordance  with  the  method  described  for  coal  in  the  Journal  of 
the  American  Chemical  Society,  1899,  Vol.  21,  page  1116.  One 
gram  of  the  material  free  from  water  is  placed  in  a  platinum 
crucible  weighing  from  20  to  30  grams  and  having  a  tightly 
fitting  cover.  It  is  then  heated  over  the  full  flame  of  a  Bunsen 
burner  for  seven  minutes.  The  crucible  should  be  supported 

*  Mun.  Engineering,  Vol.  XXXV,  No.  6,  p.  349. 


364  DUST   PREVENTIVES   AND    ROAD   BINDERS 

on  a  platinum  triangle  with  the  bottom  6  to  8  cms.  above  the 
top  of  the  burner.  The  flame  should  be  fully  20  cms.  high  when 
burning  free,  and  the  determination  should  be  made  in  a  place 
free  from  drafts.  The  upper  surface  of  the  cover  should  burn 
clear,  but  the  under  surface  should  remain  covered  with  carbon. 

The  residue  minus  the  small  impurity  of  ash  in  the  pure 
bitumen  is  the  fixed  carbon,  which  should  be  calculated  to  100 
per  cent,  with  the  volatile  hydrocarbons,  excluding  the  inor- 
ganic matter. 

(Value  of  test.)  The  fixed  carbon  determination  shows  much 
the  same  thing  as  that  for  naphtha  insoluble  bitumen,  as  it 
serves  as  an  indication  of  the  mechanical  stability  of  an  oil. 
Paraffin  oils  show  but  little  fixed  carbon,  while  the  asphaltic 
oils  run  higher  and  the  asphalts  still  higher.  The  terms  fixed 
carbon  and  free  carbon  should  not  be  confused,  as  they  have 
entirely  different  meanings.  Free  carbon  always  exists  as  such 
in  the  material,  while  fixed  carbon  is  the  coke  resulting  from 
ignition  of  the  bitumen  in  the  absence  of  oxygen.  Fixed  car- 
bon determinations  are  seldom  made  upon  tars,  as  the  presence 
of  free  carbon  interferes  with  this  test.  Owing  to  a  miscon- 
ception as  to  what  fixed  carbon  represents,  specifications  have 
sometimes  been  made  limiting  the  percentage  of  this  substance 
to  a  very  low  figure.  Providing  that  free  carbon  is  absent,  com- 
paratively high  percentages  of  fixed  carbon  are  a  rather  desirable 
property  in  oils,  for  the  reason  before  mentioned,  especially  if  they 
are  to  be  used  in  construction  work.  Native  asphalts  average 
from  12  to  14  per  cent.  No  asphaltic  cement  suitable  for  con- 
struction work  according  to  the  mixing  method  will  probably 
show  less  than  6  per  cent  fixed  carbon,  but  too  great  reliance 
should  not  be  placed  upon  this  determination,  as  it  is  not  a 
very  accurate  one  and  is  employed  more  as  a  means  of  identifi- 
cation and  as  a  comparative  test  for  the  naphtha  insoluble 
material  than  for  any  other  purpose. 

Paraffin  Scale.  —  (Method.)  This  determination  may  be 
made  upon  oil  products  according  to  the  method  employed  by 
the  Standard  Oil  Company. 


EXAMINATION   OF   BITUMINOUS    ROAD   MATERIALS       365 


"One   hundred   grams  of    the  oil   is    distilled    rapidly  in  a 
6  ounce  retort  to  dry  coke. 

"Five  grams  of  the  well-mixed  distillate  is  treated  in  a 
2  ounce  flask  with  25 
cc.  Squibb 's  ether; 
after  mixing  together 
thoroughly,  25  cc. 
Squibb's  absolute 
alcohol  is  added,  and 
the  flask  packed 
closely  in  a  freezing 
mixture  of  finely 
crushed  ice  and  salt 
for  at  least  thirty 
minutes.  Filter  off 
the  precipitate  quick- 
ly by  means  of  a 
suction  pump,  using 
a  No.  575  C.  S.  & 
S.  Q-cm.  hardened 
filter,  cooled  by  the 
above  freezing  mix- 
ture in  a  suitable 
apparatus. 

"  Rinse  and  wash 
the  precipitate  with 
i  to  i  Squibb's 
alcohol  and  ether 
mixture  cooled  to  o° 
F.  until  free  from 
oil.  Fifty  cc.  of 
the  washing  solution 
is  usually  su in- 
dent. When  sucked 


FlG.  47.     Filtering  Apparatus  for  the  Deter- 
mination of  Paraffin  Scale. 


dry,   remove   the   paper,   transfer  the  waxy  precipitate    to    a 
small    glass   crystallizing   dish.      Dry  on    a   steam   bath   and 


366  DUST  PREVENTIVES   AND   ROAD   BINDERS 

determine  the  weight  of  paraffin  scale  remaining  in  the 
dish. 

"  Weight  of  paraffin  scale  divided  by  weight  of  distillate 
taken,  and  multiplied  by  per  cent  of  total  distillate  obtained 
from  the  original  sample,  equals  per  cent  of  paraffin  scale." 

A  convenient  form  of  filtering  apparatus  is  shown  in  Fig.  47. 
The  suction  flask  carries  a  rubber  stopper  through  which  passes 
the  stem  of  a  funnel.  The  stem  of  this  funnel  also  passes 
through  a  stopper  in  the  container  which  holds  the  freezing 
mixture.  This  container  may  be  made  by  cutting  the  bottom 
from  a  bottle  of  suitable  dimensions. 

(Value  of  test.)  While  the  general  character  of  an  oil  as 
shown  by  the  base  obtained  from  the  volatilization  test  is  ordi- 
narily a  sufficient  indication  of  its  paraffin  contents,  this  deter- 
mination is  sometimes  of  value.  The  author  believes,  however, 
that  in  most  cases  it  is  unnecessary.  In  road  oils  the  heavy 
liquid  paraffins,  when  present  in  excessive  amounts,  prob- 
ably exert  a  much  more  undesirable  influence  upon  practi- 
cal results  than  the  solid  paraffins,  and  for  this  reason  it  is 
believed  that  in  most  cases  a  determination  of  the  latter  can  be 
dispensed  with.  It  is  possible  for  manufacturers  to  distill  par- 
affin oils  in  such  a  way  as  to  remove  practically  all  paraffin  wax 
from  the  residues  and  such  products  are  no  more  desirable 
than  if  the  wax  were  present. 

Distillation  Test.  —  (Method.)  This  test  is  made  upon  tars 
and  tar  products  as  follows:  From  the  specific  gravity  of  the 
tar,  taken  at  25°  C.,  the  weight  of  250  cc.  is  calculated  and  this 
amount  poured  into  a  tared  glass  retort  of  750  cc.  capacity. 
A  cork  stopper  carrying  a  thermometer  is  then  inserted  in  the 
tubulature  so  that  the  bulb  is  on  a  level  with  the  bottom  of  the 
juncture  of  stem  and  body  of  the  retort,  as  shown  in  Fig.  48. 

The  tar  should  be  heated  gradually  by  means  of  a  Bunsen 
burner  and  the  first  fraction  to  110°  C.  caught  in  a  graduated 
glass  cylinder.  A  cold  wet  towel  wrapped  about  the  stem  of 
the  retort  serves  to  condense  the  distillate.  If  the  tar  is  a 
crude  one  containing  much  water,  great  care  must  be  taken  to 


EXAMINATION   OF   BITUMINOUS   ROAD   MATERIALS       367 


FIG.  48.    Distillation  Test  Apparatus. 

prevent  it  from  boiling  over.  After  the  first  fraction  is  col- 
lected, however,  distillation  proceeds  without  trouble.  At  this 
point  the  receiver  is  changed  for  another  graduated  glass 
cylinder  and  an  asbestos  paper  cover  (see  Fig.  49)  placed  over 
the  retort  for  the  purpose  of  obtaining  a  uniform  temperature. 
The  flame  of  the  burner  should  be  so  regulated  that  not  over 


368 


DUST  PREVENTIVES   AND   ROAD   BINDERS 


: 


two  drops  of  distillate  per  second  are  collected.  At  170°  C.  the 
receiver  is  again  changed  and  a  third  fraction  to  270°  C.  col- 
lected. Distillation  is  then  stopped,  and  any  material  which 
may  have  solidified  in  the  stem  of  the  retort  is  liquified  by  the 
application  of  heat  and  caught  in  the  last  receiver.  When  the 

maximum  temperature 
is  reached  for  each  frac- 
tion the  flame  should 
be  removed  from  under 
the  retort  until  the  ther- 
mometer shows  a  drop 
of  about  5  degrees. 
The  temperature  is  then 
raised  very  slowly  to 
the  maximum  again  be- 
fore the  graduate  is 
changed  for  the  next 
fraction.  In  this  manner 
very  uniform  results 
may  be  obtained. 

If  water  was  present  in  the  tar  it  will  be  noticed  that  the 
first  fraction  separates  into  two  layers,  the  lower  of  ammoniacal 
liquor  or  water  and  the  upper  of  oil.  All  of  the  fractions  are 
cooled  to  25°  C.,  their  volume  percentage  calculated  and  that 
of  the  pitch  residue  determined  by  difference.  The  per  cent 
of  pitch  and  the  various  distillates  upon  a  weight  basis  may 
also  be  determined,  and  note  made  of  the  approximate  volume 
of  solids  which  precipitate  from  the  distillates  upon  cooling 
to  25°  C.  Distillations  carefully  conducted  according  to  the 
method  described  give  quite  comparable  results. 

The  results  obtained  are  reported  as  follows,  to  half  of  i  per 
cent: 


FIG.  49.     Asbestos  Cover  for  Retort. 

(Fold  along  dotted  lines  and  fasten  together 
with  platinum  or  copper  wire  staples.) 


1 .  Water  or  ammoniacal  liquor 

2.  First  light  oils  to  110°  C 

3.  Second  light  oils  110°  C.  to  170°  C 

4.  Heavy  or  dead  oils  170°  C.  to  270°  C 

5.  Pitch  residue  by  difference 


%  by  vol. 


by  wt. 


EXAMINATION   OF    BITUMINOUS    ROAD   MATERIALS     369 

(Value  of  test.)  The  distillation  test  as  applied  to  tars  is 
a  very  valuable  one,  both  for  the  purpose  of  ascertaining  their 
road  building  properties  and  method  of  preparation  if  they  are 
refined  products.  All  crude  tars  contain  water,  which  of  course 
appears  in  the  first  fraction  to  110°  C.  In  coal  tars  this  water 
is  ammoniacal,  while  in  water  gas  tars  it  is  not.  No  tar  con- 
taining water  should  be  employed  as  a  permanent  binder  and 
even  in  temporary  binders  its  presence  is  detrimental.  Refined 
tars  for  use  in  road  construction,  if  of  suitable  original  con- 
sistency for  permanent  work,  should  not  contain  over  7  or  8  per 
cent  by  volume  of  distillate  up  to  170°  C.,  and  this  distillate, 
together  with  that  lying  between  170°  and  270°  C.,  should  when 
cold  show  but  little  precipitated  naphthalene.  The  napthalene 
contents  of  the  last  fraction  will  often  differentiate  the  plain 
residual  coal  tar  pitches  from  cut  back  products.  In  the  former 
this  fraction  will  usually  run  from  one  quarter  to  three-quarters 
solid  naphthalene,  while  in  the  latter  it  will  run  much  lower, 
owing  to  the  fact  that  these  oils  have  been  separated  from 
naphthalene  before  using  them  as  a  flux.  Naphthalene  is  an 
undesirable  constituent  of  road  tars,  as  it  gives  the  product 
a  false  consistency  and  volatilizes  quite  readily.  It  is  usually 
found  in  coal  tars  to  a  greater  extent  than  in  water  gas  tars. 
In  all  tars  to  be  used  in  road  construction  the  total  distillate  to 
270°  C.  should  not  exceed  50  per  cent  by  volume  of  the  original 
material,  or  otherwise  the  product  will  be  deficient  in  true  bind- 
ing base,  especially  if  its  free  carbon  content  is  high.  For  sur- 
face treatment  this  distillate  may  run  higher,  as  the  lighter  oils 
are  necessary  to  give  the  tar  a  proper  degree  of  fluidity  for 
application,  especially  if  the  application  is  to  be  made  cold. 
In  cold  climates  a  high  percentage  of  heavy  oils  lying  between 
170°  C.  and  270°  C.  is  desirable,  as  they  reduce  the  brittleness  of 
the  material. 

Tars  which  have  been  simply  dehydrated  often  carry  as  high  as 
10  to  18  per  cent  of  light  oils  between  110°  C.  and  170°  C.  if  pro- 
duced by  destructive  distillation  of  coal.  Dehydrated  water 
gas  tars  will  usually  run  much  higher  in  this  respect.  These 


370  DUST  PREVENTIVES   AND   ROAD   BINDERS 

oils  are  of  no  value  for  road  purposes,  except  when  it  is  desired 
to  use  a  product  which  will  harden  rapidly  after  application. 

When  a  mixture  of  tar  and  oil  products  is  suspected,  the 
distillation  test  will  often  decide  the  matter  very  definitely.  Pe- 
troleum and  tar  distillates  obtained  between  two  given  tempera- 
tures will  vary  in  specific  gravity,  the  petroleum  distillate  being 
lighter  than  the  tar  distillate.  If  distillation  is  conducted  care- 
fully a  separation  of  these  two  products  will  often  take  place  in  the 
receiver,  forming  two  distinct  layers  of  oil.  This  will  not  happen 
if  either  a  pure  tar  or  pure  petroleum  product  is  distilled.  If 
desired,  the  separate  distillates  may  be  identified  by  suitable 
chemical  means.  Any  naphthalene  which  may  pass  over  and 
precipitate  out  of  the  distillate  is  almost  conclusive  evidence 
of  the  presence  of  tar.  Both  the  tar  and  petroleum  distillates 
have  very  characteristic  odors,  which  may  usually  be  dis- 
tinguished even  in  a  mixture  of  the  two. 

Examination  of  Bituminized  Aggregates.  —  When  it  is  desired 
to  analyze  a  bituminized  aggregate  enough  of  the  sample  to 
supply  about  60  grams  of  bitumen  is  selected  for  examination. 
Thus  if  a  mixture  contains  6  per  cent  bitumen  a  1000  gram 
sample  is  selected.  The  material  should  be  covered  and  di- 
gested for  about  twelve  hours,  in  a  suitable  dish,  with  carbon 
disulphide.  The  supernatant  liquid  is  then  decanted  off,  fresh 
solvent  added  and  the  process  repeated,  after  agitation,  until 
practically  all  of  the  bitumen  has  been  removed.  The  de- 
canted solutions  are  then  poured  through  a  large  paper  filter 
and  the  filtrate  distilled  until  the  residue  is  of  syrupy  con- 
sistency. It  is  then  poured  into  an  evaporating  dish  and  heated 
for  some  time  on  a  steam  bath,  after  which  it  is  placed  in  a  hot 
air  oven  at  not  over  100°  C.  until  the  last  traces  of  carbon 
disulphide  have  been  removed.  The  recovered  bitumen  may 
then  be  examined  in  the  usual  manner. 

The  residue  remaining  on  the  filter  should  be  dried,  ignited 
and  added  to  the  rest  of  the  mineral  matter,  after  which  a 
separation  of  the  aggregate  can  be  made  by  screening  it  into 
various  sizes. 


EXAMINATION   OF  BITUMINOUS   ROAD   MATERIALS       371 

Summary  and  Conclusions.  —  The  foregoing  description  of 
tests,  for  bituminous  road  materials  and  the  interpretation  of 
results  for  same,  should  enable  the  road  engineer  not  only  to 
make  an  intelligent  examination  of  materials  which  he  has 
occasion  to  use,  but  also  to  judge  from  such  examination  as  to 
the  value  of  any  given  material  for  a  given  purpose.  As  was 
stated  early  in  this  chapter,  a  number  of  factors  should  be  con- 
sidered when  making  an  examination,  which  may  modify  the 
method  to  some  extent.  When  a  mixture  of  tar  and  oil  or 
asphalt  is  suspected  a  somewhat  different  method  may  have  to 
be  employed  than  when  the  product  belongs  to  a  single  type; 
some  tests,  such  as  determinations  of  the  melting  point  and 
penetration  of  a  material,  cannot  always  be  made;  emulsions 
may  require  slightly  different  treatment  from  the  plain  bind- 
ers: and  the  analyst  must  therefore  exercise  some  judgment  in 
regard  to  an  examination.  In  most  cases,  however,  bituminous 
road  materials  may  be  broadly  classed  either  as  oil  or  tar  prod- 
ucts. A  list  of  those  determinations  which  the  author  considers 
most  important  for  each  class  is  given  below 


OIL  AND  ASPHALT  PRODUCTS. 

(1)  Specific  gravity 

(2)  Flash  point. 

(3)  Melting  point  of  solids. 

(4)  Penetration  of  semi  solids  and  solids. 

(5)  Volatilization  at  163°  C.  five  hours. 

a.  Melting  point  of  residue. 

b.  Penetration  of  residue. 

(6)  Solubility  in  carbon  disulphide. 

a.  Total  bitumen. 

b.  Organic  matter  insoluble. 

c.  Inorganic  matter. 

(7)  Bitumen  insoluble  in  86°  Naphtha. 

(8)  Fixed  carbon. 


372  DUST   PREVENTIVES  AND   ROAD   BINDERS 

TAR  PRODUCTS 

(1)  Specific  gravity. 

(2)  Melting  point  of  solids. 

(3)  Free  carbon. 

(4)  Results  of  distillation. 

a.  Water. 

b.  First  light  oils  to  110°  C. 

c.  Second  light  oil  no°-i7o°  C. 

d.  Heavy  oils  170°  -270°  C. 

e.  Pitch  residue. 

In  conclusion  it  may  be  said  that  under  the  interpretation  of 
results  and  value  of  test,  only  the  very  broadest  limitations 
have  been  set  with  regard  to  the  effect  of  physical  and  chemical 
properties  upon  the  suitability  of  a  material  for  a  given  pur- 
pose. This  is  due  to  the  necessarily  broad  discussion  of  the 
subject.  For  individual  cases  it  will  often  be  found  necessary 
to  draw  these  limitations  closer  if  best  results  are  to  be  obtained 
in  practice. 


CHAPTER  XIV. 

METHODS   OF  EXAMINATION  PROPOSED   OR  ADOPTED 
BY  AMERICAN   SOCIETIES. 

American  Society  for  Testing  Materials  (1909). 

REPORT  OF    COMMITTEE    H    ON    STANDARD    TESTS    FOR   ROAD 
MATERIALS. 

YOUR  committee  on  Standard  Tests  for  Road  Materials 
has  made  considerable  progress  during  the  past  year.  After 
careful  consideration,  the  method  for  the  determination  of 
bitumen  in  asphalt  paving  mixtures,  refined  asphalts  and  asphalt 
cements,  which  was  reported  and  accepted  by  the  society  in 
1906,  has  been  revised  so  as  to  include  all  bituminous  paving 
and  road  material.  It  is  believed  that  this  revision  can  be 
made  without  a  further  investigation  by  the  examination  of 
various  samples  by  members  of  the  committee  and  other 
analysts,  as  was  done  before  the  presentation  in  1906  of  the 
method  referred  to  above. 

The  committee,  in  presenting  this  method  of  analysis,  wish 
it  understood  that  they  do  not  recommend  it  as  the  best  for 
general  use,  as  it  is  longer  and  in  several  cases  gives  no  better 
results  than  other  more  expeditious  methods,  but  only  as  a 
method  to  be  resorted  to  in  case  of  dispute.  A  rapid  method, 
which  is  suggested  for  general  use,  is  also  given. 

The  committee  further  recommends  the  methods  for  sizing 
and  separating  the  aggregate  in  asphalt  paving  mixtures  and 
determining  the  consistency  of  bitumens  by  penetration,  as 
reported  to  the  society  in  1906  and  published  in  the  proceed- 
ings for  that  year. 

Methods  for  the  determination  of  the  loss  on  heating  of  oil 
and  asphaltic  compounds,  and  the  determination  of  residual 

373 


374  DUST  PREVENTIVES  AND   ROAD  BINDERS 

coke  in  bitumens,  are  herewith  submitted  to  the  society  for  the 
first  time. 

All  of  the  tests  for  bituminous  compounds  for  roads   and 
pavements  referred  to  above  follow  as  an  appendix  to  this  report. 
Respectfully  submitted  on  behalf  of  the  committee, 

LOGAN  WALLER  PAGE,  Chairman. 
PREVOST  HUBBARD,  Secretary. 


APPENDIX. 

PROPOSED  TESTS  FOR  BITUMINOUS  COMPOUNDS  FOR  ROADS  AND 
PAVEMENTS,   INCLUDING   METHOD    OF   SIZING  AND 
SEPARATING  THE  AGGREGATE  IN  ASPHALT 
PAVING  MIXTURES.* 

METHOD  FOR  THE  DETERMINATION  OF  BITUMEN  IN  PAVING  COM- 
POUNDS,  INCLUDING  THE  DETERMINATION   OF   BITUMEN 
IN  ASPHALT  PAVING  MIXTURES,  REFINED  ASPHALTS, 
ASPHALT  CEMENTS,  BITUMEN-TREATED  ROAD 
MATERIALS,   TARS  AND   TAR  PITCHES, 
SOLUBLE  IN  COLD  CARBON  DISUL- 
PHIDE  AND   OTHER 
SOLVENTS. 

Drying  the  Sample  and  Preparing  it  for  Analysis.  —  It  was 
decided,  owing  to  the  great  variety  of  conditions  met  with  in 
bituminous  compounds,  that  it  is  impossible  to  specify  any  one 
method  of  drying  that  would  be  satisfactory  in  every  case. 
It  is  therefore  supposed  that  the  material  for  analysis  has  been 
previously  dried,  either  in  the  laboratory  or  in  the  process  of 
refining  or  manufacture,  and  that  water,  if  present,  exists  only 
as  moisture  in  the  hydroscopic  form. 

The  material  to  be  analyzed,  if  hard  and  brittle,  is  ground 
and  spread  in  a  thin  layer  in  a  suitable  dish  (iron  or  nickel  will 

*  These  tests  are  recommended  by  Committee  H,  but  the  Committee  is  not  yet 
prepared  to  advise  their  adoption  as  "standards"  by  the  society. 


METHODS  PROPOSED   BY  AMERICAN  SOCIETIES  375 

answer  every  purpose)  and  kept  at  a  temperature  of  125°  C.  for 
one  hour.  In  the  case  of  paving  mixtures  and  road  materials, 
where  it  is  not  desirable  to  crush  the  rock  or  sand  grains,  a 
lump  may  be  placed  in  the  drying  oven  until  it  is  thoroughly 
heated  through,  when  it  can  be  crushed  down  into  a  thin  layer 
and  dried  as  above.  If  the  material  under  examination  con- 
tains any  hydrocarbons  at  all  volatile  at  this  temperature,  it 
will  of  course  be  necessary  to  resort  to  other  means  of  drying. 

Analysis  of  Sample. — After  drying,  from  2  to  15  grams 
(depending  on  the  richness  in  bitumen  of  the  substance)  is 
weighed  into  a  i5o-cc.  Erlenmeyer  flask,  the  tare  of  which  has. 
been  previously  ascertained,  and  treated  with  100  cc.  of  car- 
bon disulphide.  The  flask  is  then  loosely  corked  and-  shaken 
from  time  to  time  until  practically  all  large  particles  of  the 
material  have  been  broken  up,  when  it  is  set  aside  and  not  dis- 
turbed for  forty-eight  hours.  The  solution  is  then  decanted 
off  into  a  similar  flask  that  has  been  previously  weighed,  as 
much  of  the  solvent  being  poured  off  as  possible  without  dis- 
turbing the  residue.  The  first  flask  is  again  treated  with  fresh 
carbon  disulphide  and  shaken  as  before,  when  it  is  put  away 
with  the  second  flask  and  not  disturbed  for  forty-eight  hours. 

At  the  end  of  this  time  the  contents  of  the  two  flasks  are 
carefully  decanted  off  upon  a  weighed  Gooch  crucible  fitted 
with  an  asbestos  filter,  the  contents  of  the  second  flask  being 
passed  through  the  filter  first.  The  asbestos  filter  shall  be  made 
of  ignited  long-fiber  amphibole,  packed  in  the  bottom  of  a. 
Gooch  crucible  to  the  depth  of  not  over  one-eighth  inch.  After 
passing  the  contents  of  both  flasks  through  the  filter,  the  two 
residues  are  shaken  with  more  fresh  carbon  disulphide  and  set 
aside  for  twenty-four  hours  without  disturbing,  or  until  it  is 
seen  that  a  good  subsidation  has  taken  place,  when  the  solvent 
is  again  decanted  off  upon  the  filter.  This  washing  is  con- 
tinued until  the  filtrate  or  washings  are  practically  colorless. 

The  crucible  and  both  flasks  are  then  dried  at  i25°C.  and 
weighed.  The  filtrate  containing  the  bitumen  is  evaporated,  the 
bituminous  residue  burned,  and  the  weight  of  the  ash  thus 


376  DUST  PREVENTIVES  AND   ROAD   BINDERS 

obtained  added  to  that  of  the  residue  in  the  two  flasks  and  the 
crucible.  The  sum  of  these  weights  deducted  from  the  weight 
of  substance  taken  gives  the  weight  of  bitumen  extracted.  In 
the  analysis  of  hard  asphalts  or  tar  pitch  for  their  solubility  in 
carbon  disulphide  and  also  in  the  analysis  of  any  of  the  bitumens 
for  their  solubility  in  naphtha,  it  is  recommended  that  from  1 5  to 
20  grams  of  glass  beads  be  introduced  into  the  first  flask  with  the 
substance.  When  the  flask  is  shaken,  these  beads  grind  up  any 
lump  of  hard  bitumen,  and  thus  greatly  facilitate  the  solution  of 
the  soluble  constituents.  In  filtering  these  solutions  through  the 
Gooch  crucible,  they  should  be  allowed  to  run  through  by 
gravity,  as  the  application  of  an  exhaust  appears  to  cause  a 
clogging  of  the  filtering  medium. 

This  test  shall  be  carried  on  at  a  temperature  of  from  20° 
to  25°  C.  When  carbon  disulphide  or  carbon  tetrachloride  are 
used  as  solvents,  they  must  be  chemically  pure.  When  naphtha 
is  employed,  the  committee  recommends  that  in  all  cases  it  be 
described  by  stating  its  specific  gravity  and  the  temperatures 
between  which  it  distills. 


RAPID    METHOD    FOR    THE    DETERMINATION    OF    MATERIAL   IN 

BITUMINOUS    ROAD    COMPOUNDS    INSOLUBLE    IN 

COLD   CARBON   DISULPHIDE. 

For  rapid  work  the  committee  suggests  the  following  method 
as  a  convenient  one  to  be  employed.  It  is  based  in  general  upon 
the  standard  method,  and  is  applicable  to  practically  all  bitumi- 
nous compounds. 

From  one  to  ten  grams  of  the  water-free  material  (depending 
upon  the  amount  of  bitumen  present)  is  weighed  into  a  i5o-cc. 
Erlenmeyer  flask,  the  tare  of  which  has  been  previously  ascer- 
tained, and  treated  with  100  cc.  of  carbon  disulphide.  The  flask 
is  then  loosely  corked  and  shaken  from  time  to  time  until  prac- 
tically all  large  particles  of  the  material  have  been  broken  up, 
when  it  is  set  aside  for  not  less  than  fifteen  hours.  At  the  end 
of  this  time  the  contents  of  the  flask  are  decanted  off  upon  a 


METHODS   PROPOSED   BY  AMERICAN   SOCIETIES  377 

weighed  Gooch  crucible  fitted  with  a  long-fiber  amphibole  as- 
bestos filter.  The  residue  remaining  in  the  flask  is  then  washed 
with  50  cc.  of  carbon  disulphide,  allowed  to  settle,  and  decanted 
as  before,  the  insoluble  matter  being  finally  brought  upon  the 
filter  and  washed  with  100  cc.  of  carbon  disulphide,  or  until  the 
washings  are  practically  colorless.  The  filter  and  contents  are 
then  dried  at  125°  C.,  cooled,  and  weighed.  Should  any  residue 
remain  in  the  flask,  it  is  also  dried  and  weighed  and  this  weight 
added  to  that  of  the  residue  in  the  crucible.  The  filtrate  should 
be  burned  off  and  ignited  to  an  ash  and  the  weight  of  the  ash 
thus  obtained  added  to  that  of  the  insoluble  residue.  The 
weight  of  the  total  residue  deducted  from  that  of  the  original 
material  gives  the  weight  of  bitumen  soluble  in  cold  carbon 
disulphide.  In  case  of  tars  and  pitches  the  percentage  of  in- 
soluble residue,  determined  as  above,  minus  that  of  any  ash 
which  may  be  found  by  igniting  a  separate  sample,  is  reported 
as  free  carbon.  Glass  beads  may  be  employed  in  the  flask,  as 
described  in  the  standard  method  for  the  determination  of  bitu- 
men. This  test  shall  be  carried  on  at  a  temperature  of  from 
20°  to  25°  C. 


METHOD    FOR    THE    DETERMINATION    OF    THE    CONSISTENCY 
OF   BITUMEN. 

The  consistency,  or  penetration,  of  a  bitumen  shall  be  the 
distance,  expressed  in  hundredths  of  a  centimeter,  that  a  No.  2 
needle  will  penetrate  into  it  at  25°  C.  (77°  F.),  in  five  seconds  of 
time,  under  a  weight  of  100  grams,  the  needle  to  penetrate  direct 
without  friction. 


METHOD    FOR    THE    DETERMINATION    OF    THE    LOSS    ON    HEATING 
OF    OIL   AND    ASPHALTIC    COMPOUNDS. 

The  loss  on  heating  of  oil  and  asphaltic  compounds  shall  be 
determined  in  the  following  manner:  Fifty  grams  of  the  water- 
free  material  shall  be  placed  in  a  circular  tin  box  with  vertical 


378  DUST  PREVENTIVES   AND   ROAD   BINDERS 

sides,  measuring  about  one  inch  in  depth  by  two  and  three- 
eighths  inches  in  diameter,  internal  measurement.  The  pene- 
tration of  the  material  to  be  examined  shall,  if  possible,  be 
determined  at  25°  C.,  in  the  manner  heretofore  described,  and  the 
exact  weight  of  the  sample  ascertained.  The  sample  in  the  tin 
box  shall  then  be  placed  in  a  hot  air  oven,  heated  to  170°  C., 
and  kept  at  this  temperature  for  five  hours.  At  no  time  shall 
the  temperature  of  this  oven  vary  more  than  2°  C.  from  170°  C. 
When  the  sample  is  cooled  to  normal  temperature,  it  shajl  be 
weighed  and  the  percentage  of  loss  by  volatilization  reported. 
The  penetration  of  the  residue  shall  then,  if  possible,  be  deter- 
mined at  25°  C.,  in  the  manner  heretofore  described,  and  the  loss 
in  penetration  determined  by  subtracting  this  penetration  from 
the  penetration  before  heating. 


METHOD    FOR    THE    DETERMINATION    OF    RESIDUAL   COKE    IN 
BITUMINOUS   COMPOUNDS. 

This  determination  shall  be  made  according  to  the  method 
described  for  coal  in  the  Journal  of  the  American  Chemical 
Society,  1899,  Vol.  21,  page  1116.  This  method  is  as  follows: 
Place  i  gram  of  pure  bitumen,  free  from  water,  in  a  "  platinum 
crucible  weighing  20  to  30  grams  and  having  a  tightly  fitting 
cover.  Heat  over  the  full  flame  of  a  Bunsen  burner  for  seven 
minutes.  The  crucible  should  be  supported  on  a  platinum 
triangle  with  the  bottom  6  to  8  cms.  above  the  top  of  the  burner. 
The  flame  should  be  fully  20  cms.  high  when  burning  free,  and 
the  determination  should  be  made  in  a  place  free  from  drafts. 
The  upper  surface  of  the  cover  should  burn  clear,  but  the  under 
surface  should  remain  covered  with  carbon." 

The  residue  minus  the  small  impurity  of  ash  in  the  pure  bitu- 
men is  the  fixed  carbon,  which  snould  be  calculated  to  100  per 
cent  with  the  volatile  hydrocarbons,  excluding  the  inorganic 
matter. 


METHODS  PROPOSED  BY  AMERICAN  SOCIETIES  379 

METHOD  OF  SIZING  AND  SEPARATING  THE  AGGREGATE  IN  ASPHALT 
PAVING  MIXTURES. 

The  method  consists  of  passing  the  mineral  aggregate  through 
several  sieves  of  the  following  sizes: 

Diameter,  in  inches. 

10  meshes  per  linear  inch,  size  of  wire 0.027 

20        "         "         "       "         "  "    0.0165 

30        "         "         "       "         "  "    0.01375 

40        "         "         "       "         "  "    0.01025 

50        "         "         "       «         "  "    0.009 

80        "         "         "       "         "  "    0.00575 

100        "         "         "       "         "  "    0.0045 

200  "  "  "          "  "  "     0.00235 


weighed  Gooch  crucible,  fitted  witn  an  asuesiob  pa,u,  oijjm6 
to  constant  weight,  and  weighing  the  insoluble  residue;  then 
igniting  crucible  until  all  carbon  is  burned  off,  weighing  the 
residue  (ash).  The  difference  between  the  second  and  third 


378  DUST  PREVENTIVES   AND   ROAD   BINDERS 

sides,  measuring  about  one  inch  in  depth  by  two  and  three- 
eighths  inches  in  diameter,  internal  measurement.  The  pene- 
tration of  the  material  to  be  examined  shall,  if  possible,  be 
determined  at  25°  C.,  in  the  manner  heretofore  described,  and  the 
exact  weight  of  the  sample  ascertained.  The  sample  in  the  tin 
box  shall  then  be  placed  in  a  hot  air  oven,  heated  to  170°  C., 
and  kept  at  this  temperature  for  five  hours.  At  no  time  shall 
the  temperature  of  this  oven  vary  more  than  2°  C.  from  170°  C. 
When  the  sample  is  cooled  to  normal  temperature,  it  shajl  be 
weighed  and  the  percentage  of  loss  by  volatilization  reported. 
The  penetration  of  the  residue  shall  then,  if  possible,  be  deter- 
mined at  25°  C.,  in  the  manner  heretofore  described,  and  the  loss 

this  Denetration  from 


ERRATA. 

Page  379,  for  revised  methods 
adopted  by  the  Special  Committee  on 
Bituminous  Materials  for  Road  Con- 
struction, read  : 

"  Revised  methods  proposed  by  the 
Special  Committee  on  Bituminous 
Materials  for  Road  Construction." 


cent  with  the  volatile   hydrocarbons,  excluding   the  inorganic 
matter. 


METHODS   PROPOSED   BY  AMERICAN  SOCIETIES 


379 


METHOD  OF  SIZING  AND  SEPARATING  THE  AGGREGATE  IN  ASPHALT 
PAVING  MIXTURES. 

The  method  consists  of  passing  the  mineral  aggregate  through 
several  sieves  of  the  following  sizes: 

Diameter,  in  inches. 

10  meshes  per  linear  inch,  size  of  wire 0.027 

0.0165 

0.01375 

0.01025 

o . 009 

0.00575 

0.0045 


20 

3° 
40 

5° 

80 

100 

200 


0.00235 


American  Society  of  Civil  Engineers 

REVISED   METHODS    ADOPTED   BY    THE    SPECIAL   COMMITTEE    ON 
BITUMINOUS   MATERIALS   FOR   ROAD   CONSTRUCTION. 

W.  W.  CROSBY,  Chairman. 


A.  H.  BLANCHARD,  Secretary. 


TARS. 


Water-Soluble  Materials. —  Boil  gently  two  grams  of  material 
with  25  cc.  of  distilled  water  for  one  hour.  Filter  and  wash 
with  25  cc.  of  boiling  water.  Evaporate  nitrate  in  weighed 
dish  to  dryness  and  constant  weight  at  105°  C.  Weigh  residue. 
Ignite  residue  and  weigh  again,  giving  weight  of  inorganic 
matter  plus  weight  of  crucible.  Weight  No.  2  minus  weight 
No.  3  gives  weight  of  organic  matter. 

Specific  Gravity.  —  Use  some  standard  form  of  pycnometer. 
Material  and  distilled  water  must  have  a  temperature  of  25°  C. 

For  semisolid  and  solid  materials  use  Sommer's  pycnometer. 

Free  Carbon.  —  The  free  carbon  shall  be  determined  by 
dissolving  for  fifteen  hours  two  grams  of  the  compound  in  ioocc. 
of  cold  carbon  bisulphide,  filtering  the  solution  through  a 
weighed  Gooch  crucible,  fitted  with  an  asbestos  pad,  drying 
to  constant  weight,  and  weighing  the  insoluble  residue;  then 
igniting  crucible  until  all  carbon  is  burned  off,  weighing  the 
residue  (ash),  The  difference  between  the  second  and  third 


380  DUST  PREVENTIVES   AND   ROAD   BINDERS 

weights  is  "free  carbon."  The  difference  between  first  and 
third  is  ash,  which  should  be  noted. 

Fixed  Carbon.  —  About  one  gram  of  the  compound  is  weighed 
into  a  platinum  crucible  one  and  one-eighth  to  one  and  one-half 
inches  high.  The  crucible  with  the  lid  on  is  heated,  first  gently, 
and  then  until  no  more  smoke  and  flame  issues  between  the 
crucible  and  the  lid.  It  is  then  heated  three  and  one-half 
minutes  in  the  full  heat  of  the  burner;  then  cooled  and  weighed. 
The  crucible  lid  is  then  removed  and  the  crucible  and  contents 
allowed  to  remain  in  the  full  heat  of  the  burner  until  the  carbon 
is  burned  off,  and  then  weighed  again.  The  difference  between 
these  two  weights  is  the  fixed  carbon. 

Evaporation.  —  Twenty  grams  of  compound  are  heated  in  a 
flat-bottomed  dish,  two  and  one-half  inches  in  diameter  and 
about  one  inch  high,  for  a  total  of  five  hours  in  three  succes- 
sive periods  of  three,  one  and  one  hours,  respectively,  in  an 
oven,  the  interior  of  which  is  maintained  at  a  uniform  and 
constant  temperature  of  170°  C.  This  oven  is  to  be  controlled 
by  any  thermo  regulator,  controlling  within  two  degrees,  and 
is  to  have  its  full  temperature  before  the  compound  is  intro- 
duced. The  dish  must  be  level.  Remove  dish  from  oven  and 
stir  contents  thoroughly  for  one  minute  between  successive 
periods. 

Penetration  of  Residue  from  Evaporation  Tests.  —  The  pene- 
tration shall  be  measured  by  a  standard  machine  using  100 
grams  load  and  No.  2  needle.  Use  a  flat-bottomed  glass  dish 
seven-eighths  of  an  inch  in  diameter  and  one  and  one-half 
inches  in  height.  Fill  flush  with  top  with  material  and  allow 
same  to  stand  at  room  temperature  for  one-half  hour.  Im- 
merse in  water  bath,  covering  material  for  one  hour.  Im- 
merse needle  to  be  used  for  five  minutes  in  same  bath.  Test 
at  once,  making  three  determinations.  The  recorded  pene- 
tration will  be  the  average  value.  Temperature  4°  C.  and 

25°  c. 

(Note):  Residue  must  be  melted  at  lowest  possible  tem- 
perature and  thoroughly  mixed  in  by  stirring. 


METHODS   PROPOSED   BY   AMERICAN   SOCIETIES  381 

Melting  Point  of  Residue  from  Evaporation.  —  The  material 
whose  melting  point  is  to  be  determined  is  melted  and  poured 
into  a  mold  that  will  make  a  one-half  inch  cube.  A  No.  10 
gauge  wire  about  six  to  eight  inches  long  is  bent  at  right  angles 
for  a  length  of  three-quarter  inch  at  one  end  and  the  center  of  the 
cube  is  placed  on  this  end  so  that  one  of  the  diagonals  of  the 
vertical  face  of  the  cube  is  parallel  to  the  long  part  of  wire. 
Take  a  bottle  of  a  size  about  two  inches  in  diameter  and  four 
inches  high  and  place  a  piece  of  white  paper  in  the  bottom  of  it. 
Pass  the  long  part  of  the  wire  through  the  cork  of  the  bottle 
so  that  the  lower  edge  of  the  cube  will  be  within  one  inch  of 
the  bottom  of  the  bottle.  Also  put  a  thermometer  through  the 
cork  so  that  the  bulb  is  opposite  the  cube.  Place  the  bottle 
in  a  water  or  oil  bath  and  raise  the  temperature  of  the  bath 
at  a  rate  of  three  to  six  degrees  C.  a  minute.  The  melting  point 
of  the  material  is  the  temperature  of  the  thermometer  inside 
the  bottle  at  the  time  that  the  material  touches  the  paper  in  the 
bottom  of  the  bottle. 

Distillation.  - 

Up  to  105°  C. 

From  105°  to  170°  C. 

From  170°  to  225°  C. 

From  225°  to  270°  C. 

From  270°  to  300°  C. 

Seven  hundred  grams  of  the  compound  are  weighed  into  a 
retort  (E.  &  A.  four  pints  No.  4521),  whose  top  is  fitted  with 
a  tee  as  close  as  possible  to  the  retort,  and  a  condenser  pipe 
twenty-four  to  thirty-six  inches  long;  the  upper  branch  of 
the  tee  is  used  for  the  insertion  of  a  thermometer,  the  top  of 
whose  bulb  is  placed  immediately  below  the  main  outlet,  of 
the  tee. 

Viscosity  or  Consistency.  —  Temperatures  at  which  viscosities 
will  be  determined  are  100°  C.  and  25°  C. 

Penetrometer  to  be  used  in  accordance  with  standard  method 
on  materials  solid  at  above  temperatures.  On  materials  which 
at  the  above  temperature  the  penetrometer  cannot  be  used, 


382  DUST  PREVENTIVES  AND   ROAD   BINDERS 

the  viscosity  shall  be  determined  by  one  of  the  following  instru- 
ments : 

Engler  Viscosimeter. 

Lunge  Tar  Tester. 

New  York  Testing  Laboratory  Viscosimeter. 


COMPOUNDS    PREPARED    FROM   PETROLEUM   OR   NATURAL  ASPHALT 

PITCHES. 

Melting  Point  of  Solid  Asphalts. —  Same  method  as  for  resi- 
due from  evaporation  of  tars. 

Water-Soluble  Materials.  —  Same  method  as  for  tars. 

Specific  Gravity.  —  Same  method  as  for  tars. 

Free  Carbon.  —  Same  method  as  for  tars. 

Material  Soluble  in  Cold  Carbon-Tetrachloride.  —  Same  method 
as  for  free  carbon,  except  carbon-tetrachloride  is  used  as  a 
solvent  instead  of  carbon-bisulphide. 

Fixed  Carbon.  —  Same  method  as  for  tars. 

Paraffin.  —  One  hundred  grams  or  less  of  the  compound  is 
distilled  rapidly  in  a  retort  to  dry  coke. 

Five  grams  of  the  well  mixed  distillate  is  treated  in  a  two- 
ounce  flask  with  25  cc.  Squibbs  absolute  ether;  after  mixing 
thoroughly,  25  cc.  Squibbs  absolute  alcohol  is  added  and  the 
flask  packed  closely  in  a  freezing  mixture  of  finely  crushed  ice 
and  salt  for  at  least  30  minutes.  Filter  the  precipitate  quickly 
by  means  of  a  suction  pump,  using  a  No.  575  C.  S.  &  S.  9  c.m. 
hardened  filter  paper.  Rinse  and  wash  the  flask  and  precipi- 
tate (with  i  to  i  Squibbs  alcohol  and  ether  mixture  cooledvto 
—  17°  C.)  until  free  from  oil  (50  cc.  of  washing  solution  is 
usually  sufficient).  When  sucked  dry  remove  paper,  transfer 
waxy  precipitate  to  small  glass  dish,  evaporate  on  steam  bath 
and  weigh  paraffin  remaining  on  dish. 

Calculation.  —  Weight  of  paraffin  divided  by  weight  of 
distillate  taken  and  multiplied  by  per  cent  of  total  distillate 
used  from  original  sample,  equals  per  cent  of  paraffin. 

Evaporation  Test  No.  1.  —  Same  method  as  for  tars. 


METHODS   PROPOSED   BY  AMERICAN  SOCIETIES  383 

Penetration  of  Residue  from  Evaporation  Test  No.  1.  —  Same 
method  as  for  similar  residue  of  tars. 

Melting   Point  of  Residue  from   Evaporation   Test   No  1.  - 
Same  method  as  for  similar  residue  of  tars. 

Solubility  in  88°  Baume  Naphtha.  —  Two  grams  of  com- 
pound are  placed  in  four-ounce  oil  sample  bottle  made  up  to  100 
cc.  with  88°  B.  naphtha,  having  a  boiling  point  between  40° 
C.  and  55°  C.,  the  whole  well  shaken  until  compound  is  broken 
up.  The  bottle  is  then  centrifugalized  for  ten  minutes,  50  cc. 
are  withdrawn  into  a  weighed  flask,  the  naphtha  distilled  by  a 
water  bath  and  the  residue  weighed.  Another  ten  cc.  of  the 
naphtha  solution  is  run  over  three  and  one-half  inches  Petri 
glass  and  allowed  to  evaporate  for  twenty-four  hours  at  room 
temperature.  Note  character  of  residue,  i.e.,  sticky  or  oily. 

Viscosity  or  Consistency.  —  Same  as  for  tars. 

Evaporation  Test  No.  2.  —  Same  method  as  for  tars  except 
oven  temperature  shall  be  205°  C. 

Penetration  of  Residue  from  Evaporation  Test  No.  2.  —  Same 
method  as  for  tars. 

Melting  Point  of  Residue  from  Evaporation  Test  No.  2.  — 
Same  method  as  for  tars. 


CHAPTER  XV 
SELECTION  OF  DUST  PREVENTIVES  AND  ROAD  BINDERS. 

MOST  of  the  factors  which  should  govern  the  selection  of  dust 
preventives  and  road  binders  have  at  one  time  or  another  been 
discussed  in  previous  chapters,  but  so  many  instances  have  come 
under  the  author's  notice  where  failures  have  resulted  from  the 
exercise  of  poor  judgment  in  selection,  that  it  seems  well  to 
close  this  book  with  a  short  chapter  on  this  most  important 
subject.  It  is  undoubtedly  true  that  thousands  of  dollars  are 
wasted  annually  in  a  repetition  of  experiments  which  time  and 
again  have  proved  costly  mistakes.  On  the  other  hand  experi- 
ments which  have  given  good  results  in  some  places  have  also 
proved  failures  when  tried  in  different  localities.  The  whole 
subject  is  as  yet  in  an  experimental  stage  and  much  confusion 
has  arisen  over  the  contradictory  results  obtained  by  various 
experimenters  working  with  apparently  the  same  material. 
There  would  seem  to  be  three  main  factors  to  be  considered  in 
this  connection,  any  one  of  which  might  account  for  such  discrep- 
ancies. They  are : 

(1)  Differences  in  the  physical  and  chemical  characteristics 
of  materials  which  are  sold  under  the  same  trade  name  or  which 
are  known  only  as  types. 

(2)  Differences  in  methods  of  application. 

(3)  Differences  in  local  conditions,  to  which  the  roads  are 
subjected. 

It  is  of  course  evident  that  the  road  builder  has  no  control 
over  local  conditions  to  which  a  road  is  subjected,  but  in  the 
selection  and  application  of  the  binding  medium  to  meet  these 
conditions  he  should  exercise  considerable  judgment.  Close 
observation  and  practical  experience  have  convinced  the  author 
that  certain  fundamental  principles  have  generally  been  over- 

384 


SELECTION   OF  DUST  PREVENTIVES   AND   ROAD  BINDERS       385 

looked  or  disregarded  in  this  connection,  and  that  this  is  the 
cause  of  a  large  percentage  of  failures. .  It  is  necessary,  there- 
fore, that  not  only  the  experience  of  others  be  considered,  but 
that  some  thought  be  given  to  the  probable  effect  of  local  con- 
ditions upon  the  results  which  have  in  general  been  obtained. 
The  importance  of  ascertaining  the  composition  and  quality  of 
the  material  has  already  been  dwelt  upon  at  some  length,  but 
while  these  are  most  important  points,  they  are  not  the  only 
ones  to  be  taken  into  account,  and  it  will  be  found  that  differences 
in  local  conditions  are  factors  of  too  much  importance  to  be  dis- 
regarded. Great  differences  in  conditions  have  of  course  gen- 
erally been  considered,  but  it  is  not  always  those  clearly  apparent 
that  cause  the  greatest  variance  in  results.  It  is  this  fact  that 
makes  it  impracticable  to  frame  satisfactory  specifications  which 
may  be  considered  as  standard  for  even  a  single  individual  type 
of  binder,  to  be  applied  in  a  given  manner. 

Owing  to  lack  of  sufficient  data  by  experimenters,  it  is  often 
a  hard  matter  to  correlate  the  results  obtained  in  practice  to 
their  actual  causes,  but  certain  facts  are  indicated  which  if 
properly  considered  should  be  of  some  value  to  the  experimenter 
who  has  not  already  learned  by  experience  what  material  is  best 
suited  for  the  road  he  has  occasion  to  treat.  It  is  the  author's 
purpose  here  to  present  these  facts  in  such  form  as  to  serve  as 
a  general  guide  in  the  selection  of  material,  but  it  should  be  under- 
stood that  they  are  of  use  as  a  guide  only  and  in  no  sense  are  to 
be  considered  as  hard  and  fast  rules.  In  many  instances  the 
selection  of  a  road  binder  may  be  influenced  by  a  combination 
of  conditions  which  would  be  impossible  to  foresee  except  in 
individual  cases.  Sometimes  a  choice  may  seem  to  be  equally 
divided  among  a  number  of  materials,  and  experiment  alone 
will  determine  which,  if  any,  is  the  most  suitable.  In  many 
cases  the  experimenter  is  handicapped  by  lack  of  funds,  so  that 
the  most  suitable  material  cannot  always  be  obtained.  In  these 
cases  a  less  suitable  material  will  have  to  be  employed,  although 
in  the  long  run  this  will  often  prove  more  costly.  Except  in  rare 
instances  economy  is  the  most  important  point  to  be  considered 


386  DUST  PREVENTIVES   AND   ROAD   BINDERS 

and  while  permanency  of  results  is  often  synonymous  with 
economy  it  is  not  always  so. 

The  division  of  dust  preventives  and  road  binders  into  three 
classes,  temporary,  semipermanent  and  permanent,  suggests  in  a 
general  way  the  first  point  that  should  -be  considered  in  regard 
to  selection.  Taken  in  connection  with  the  three  great  classes 
of  roads,  county,  suburban  and  city,  it  is  at  once  evident  that 
under  ordinary  conditions  only  the  semipermanent  and  per- 
manent binders  are  suited  to  the  first  of  these  for  the  reason  that 
it  is  impracticable  to  treat  long  stretches  of  country  road  at  com- 
paratively short  intervals  of  time.  When  employing  temporary 
binders  the  road  should  not  only  be  under  constant  observation, 
so  that  applications  may  be  made  whenever  necessary,  but  facil- 
ities should  be  such  that  the  work  may  be  quickly  and  efficiently 
performed.  It  is  seldom  that  this  condition  of  affairs  exists  on  a 
country  road.  With  respect  to  suburban  and  city  roads  and 
streets,  however,  no  such  restrictions  exist  in  the  majority  of 
cases,  and  any  or  all  classes  of  binders  may  be  selected. 

Selection  of  Materials  for  Treating  Country  Roads.  —  Country 
roads  may  be  divided  into  two  general  classes,  hard  and  soft 
roads.  The  first  class  is  represented  by  the  macadam  and 
other  broken-stone  roads  and  the  second  by  earth  roads.  Sand 
and  gravel  roads  may  also  be  included  in  the  latter  class, 
although  in  many  cases  they  more  nearly  approach  the  broken- 
stone  roads  in  point  of  hardness.  In  the  case  of  hard  roads  a 
choice  of  either  oil  or  tar  products  will  exist,  but  in  the  treat- 
ment of  soft  roads  oils  only  have  so  far  proved  successful,  and 
except  for  purely  experimental  purposes  the 'choice  is  limited  to 
this  class  of  material. 

The  selection  of  a  binder  for  use  on  a  rural  macadam  road  will 
depend  upon  several  conditions.  The  first  of  these  would 
ordinarily  be  the  relative  cost  at  the  given  location.  Other 
factors,  such  as  relative  quality  of  the  available  materials,  avail- 
able apparatus  for  applying  same,  funds  available  for  treat- 
ment, climatic  conditions,  condition  of  the  road,  character  of 
the  road  stone,  and  amount  and  quality  of  traffic  to  which  the 


SELECTION   OF  DUST  PREVENTIVES  AND   ROAD  BINDERS      387 

road  is  subjected,  should  also  be  taken  into  account  and  the 
method  of  application  with  reference  to  these  conditions  should 
be  carefully  considered.  In  view  of  the  fact  that  most  work  of 
this  kind  has  not  been  planned  or  carried  out  with  sufficient 
forethought,  a  hypothetical  example  may  be  considered,  even  at 
risk  of  entering  into  too  great  detail.  The  necessity  of  clearly 
illustrating  this  matter  has  been  made  evident  to  the  author, 
not  only  from  reviewing  published  descriptions  of  experiments, 
but  from  actual  work  along  these  lines. 

For  example,  let  us  suppose  that  a  stretch  of  rural  macadam 
is  to  be  treated  with  regard  to  dust  suppression.  Our  first 
effort  would  be  to  determine  if  possible  any  one  predominant 
cause  for  excessive  dust  formation.  Upon  investigation  we 
might  find  that  the  road  stone  showed  no  cementing  qualities, 
and  if  the  road  was  exposed  to  but  little  motor  traffic  a  top 
dressing  of  some  good  binding  rock  screenings  might  solve  the 
problem  quite  satisfactorily.  On  the  other  hand,  if  motor 
traffic  was  heavy  we  should  have  to  resort  to  the  use  of  a 
special  binder,  as  no  stone  road  has  so  far  proved  able  to  suc- 
cessfully withstand  the  action  of  heavy  mixed  traffic.  With 
regard  to  a  choice  of  these  materials  we  should  first  ascertain 
which  is  most  readily  available  at  a  reasonable  cost.  If  a  refined 
tar  produced  at  a  low  temperature  and  containing  a  fair  amount 
of  good  pitch  base  could  be  obtained  it  might  be  tentatively 
chosen.  In  some  localities  an  asphaltic  or  semiasphaitic  oil 
might  be  more  readily  available,  or  a  residual  oil  preparation, 
but  in  any  event  we  should  ascertain  in  so  far  as  possible 
the  particular  properties  of  the  material  which  we  are  con- 
sidering and  unconditionally  reject  those  which,  for  reasons 
that  have  already  been  discussed,  are  almost  sure  to  prove 
unsatisfactory.  Thus  a  high  carbon  tar,  a  paraffin,  petroleum 
or  a  badly  cracked  residuum  would  be  at  once  discarded,  no 
matter  how  cheap  or  readily  available  it  might  be. 

If  climatic  conditions  were  such  that  a  surface  application 
would  be  unlikely  to  last  throughout  the  winter,  and  we  were 
unable  to  rebuild  the  road  so  as  to  make  it  a  bituminous  mac- 


388  DUST  PREVENTIVES  AND  ROAD  BINDERS 

adam,  it  would  prove  most  economical  to  apply  only  sufficient 
material  to  last  throughout  the  dusty  season.  In  this  case  a 
cold  application  of  coal  tar  diluted  with  sufficient  water  gas 
tar  or  oil  tar  to  give  it  the  proper  fluidity  might  be  made, 
or  a  crude  semiasphaltic  petroleum  used  in  preference  to  a 
more  expensive  residuum  or  cut  back  product.  In  climates 
where  a  long  succession  of  alternate  frosts  and  thaws  occur 
throughout  the  winter,  accompanied  by  cold  rains,  a  treatment 
of  this  sort  will  prove  far  less  expensive  than  a  surface  appli- 
cation of  heavier  binding  material.  Under  more  favorable 
conditions,  however,  this  would  not  be  true,  and  applications 
of  tar  or  oil  requiring  heat  might  be  more  economical.  The 
conditions  of  the  road  will  often  indicate  the  method  of  treat- 
ment and  kind  of  material  which  should  be  employed.  If  the 
road  is  in  fairly  good  condition  a  surface  application  is  often 
all  that  is  required.  Where  the  road  is  badly  torn  up  and 
ravelled,  however,  it  will  often  prove  better  policy  in  the  long 
run  to  reconstruct  it  with  the  addition  of  a  bituminous  matrix 
or  else  to  resurface  it  with  a  heavy  coat  of  bitumen  covered  stone. 
In  a  case  of  this  sort  a  good  refined  tar  is  to  be  preferred  unless 
a  very  heavy  semiasphaltic  or  asphaltic  oil  can  be  secured.  If 
either  material  can  be  obtained  the  character  of  the  road  stone 
may  decide  in  favor  of  one  or  the  other.  A  hard  but  somewhat 
porous  rock  is  to  be  preferred  in  either  case,  but  perhaps  more 
particularly  in  that  of  tar,  which  is  less  easily  absorbed  than  oil. 
The  choice  of  binders  for  soft  country  roads  is'  somewhat 
restricted,  owing  to  the  fact  that  oil  only  can  be  employed. 
For  the  softer  roads  an  oil  containing  even  a  relatively  small 
amount  of  paraffin  base  is  valueless  as  a  permanent  binder, 
and  we  are  thus  narrowed  down  to  a  choice  between  the  ex- 
ceptionally good  semiasphaltic  oils,  the  true  asphaltic  oils  and 
the  residuums  and  cut  back  products  obtained  from  each. 
That  oil  containing  the  greatest  amount  of  asphaltic  base  is 
usually  to  be  preferred,  although  not  always.  In  the  case  of 
ordinary  earth,  clay  or  loam  roads  the  presence  of  a  greater 
amount  of  true  oil  is  required  than  in  that  of  sand  and  gravel 


SELECTION  OF  DUST  PREVENTIVES  AND   ROAD  BINDERS       389 

roads,  in  order  to  prevent  the  surface  from  becoming  powdery 
under  the  action  of  traffic.  Badly  cracked  residuums  should  be 
avoided,  even  to  the  extent  of  using  a  crude  oil  containing  less 
asphaltic  base.  A  very  clayey  soil  should  be  modified  by  the 
addition  of  sand  before  treatment,  and  as  has  been  noted, 
measures  should  be  taken  to  overcome  the  effect  of  alkali  soils 
upon  the  oil  used.  Methods  of  application  suitable  to  various 
conditions  have  been  discussed  elsewhere  and  need  not  be  con- 
sidered here.  Where  gravel  roads  are  to  be  treated  it  is  not 
always  necessary  to  employ  an  extremely  heavy  asphaltic  oil, 
although  such  a  material  is  to  be  preferred.  Where  fairly 
heavy  crude  semiasphaltic  or  residual  oils  can  be  obtained  at 
a  low  figure  they  may  often  be  used  to  advantage.  And  while 
the  results  may  not  be  quite  so  permanent  the  reduction  in  cost 
as  compared  with  the  truly  asphaltic  oils  will,  under  present 
conditions,  more  than  compensate  this  difference,  especially  in 
our  eastern  states. 

Where  it  is  decided  to  construct  an  earth  road  with  an  oil 
binder,  it  would  for  most  cases  be  bad  practice  to  select  a  fluid 
semiasphaltic  oil  residuum  containing  no  appreciable  amount  of 
volatile  oils,  and  yet  this  is  often  done.  The  author  has  in  mind 
an  instance  where  such  an  oil  was  selected  for  this  purpose  and 
first  applied  at  the  rate  of  one  gallon  per  square  yard  to  the 
depth  of  six  inches  in  a  very  approved  manner  so  far  as  incor- 
porating the  binder  with  the  earth  was  concerned.  The  results 
were  somewhat  disappointing  to  the  experimenter,  although 
exactly  what  should  have  been  expected  from  such  a  product. 
The  oil  being  very  fluid  was  completely  absorbed  by  the  earth, 
and  as  it  had  but  little  original  binding  value  and  was  incapable 
of  improving  in  this  respect,  no  visible  effect  was  produced 
other  than  that  the  road  became  somewhat  less  dusty  and  its 
color  was  made  slightly  darker.  The  experimenter  rightly 
inferred  that  sufficient  binder  had  not  been  employed  and 
decided  to  apply  another  gallon  per  square  yard.  He  made  the 
mistake,  however,  of  again  using  the  same  fluid  residuum. 
This  time  the  road  was  made  absolutely  dustless,  but  it  was  soft 


390  DUST  PREVENTIVES  AND   ROAD   BINDERS 

and  mealy  and  refused  to  bond  and  consolidate  under  the  roller. 
It  also  showed  signs  of  sweating  under  the  action  of  sun  and 
traffic.  This  should  have  been  a  warning,  but  as  the  road  had 
not  bonded  satisfactorily  he  thought  that  perhaps  an  additional 
gallon  of  oil  per  square  yard  would  put  it  in  good  condition. 
The  third  gallon  was,  therefore,  applied,  but  the  soil  having 
become  practically  saturated  with  the  first  two  applications 
refused  to  take  up  the  third,  and  sweated  so  badly  that  the  sur- 
face became  soft  and  gummy,  the  oil  was  tracked  by  pedestrians, 
spattered  upon  vehicles  and  their  occupants  and  in  fact  became  a 
general  nuisance,  which  was  a  hundredfold  worse  in  wet  weather. 
It  was  then  thought  that  the  application  of  broken  stone  might 
remedy  the  trouble.  Accordingly  two  or  three  inches  of  number 
two  crushed  stone  were  applied  and  rolled  into  the  road.  The 
stone  was  pushed  out  of  sight  just  as  though  it  had  been  laid 
upon  a  wet  clay  foundation,  and  the  supersaturated  oiled  earth 
coming  to  the  top  produced  the  same  condition  of  affairs  as 
before.  Eventually  the  whole  surface  had  to  be  removed  and 
replaced  with  clean  broken  stone. 

This  is  only  a  single  example  of  what  has  happened  many 
times,  but  serves  to  show  how  experience  is  dearly  paid  for.  In 
this  particular  instance  the  author  was  called  upon  to  examine 
a  sample  of  the  oil  which  had  been  used.  He  found  it  to  be  a 
rather  poor  grade  of  semiasphaltic  fluid  residuum  totally  unfit 
for  any  kind  of  road  use  except  perhaps  as  a  dust  palliative  when 
applied  in  very  small  quantities  to  a  macadam  surface.  The 
general  appearance  of  the  oil  ought  almost  to  have  been  sufficient 
evidence  of  its  unfitness  for  use  in  road  construction,  but  a 
few  simple  tests,  such  as  the  loss  by  volatilization  at  163°  C., 
naphtha  insoluble  bitumen,  fixed  carbon  determinations,  etc., 
together  with  a  written  explanation,  proved  conclusively  to  the 
experimenter  the  cause  of  failure.  Since  then  he  has  had  each 
lot  of  road  binder  which  he  has  used  examined  to  determine  its 
fitness  to  meet  given  conditions  and  is  no  longer  dependent  upon 
the  word  of  the  manufacturer  or  sales  agent  as  to  the  quality  of 
material  which  he  purchases. 


SELECTION   OF  DUST  PREVENTIVES  AND  ROAD  BINDERS      391 

Selection  of   Materials  for    Treating    Suburban    Roads.  —  A 

wider  selection  of  dust  preventives  and  binders  is  possible  in  the 
treatment  of  suburban  than  in  country  roads.  Here  all  types  of 
road  binders  may  compete,  and  it  is  often  a  difficult  matter  to 
choose  the  best  material.  As  a  rule,  hard  roads  predominate  in 
suburban  districts  and  it  is  mainly  the  selection  of  material 
for  the  treatment  of  these  with  which  we  shall  have  to  deal. 
The  hard  roads,  which  are  for  the  most  part  macadam,  may  be 
considered  under  two  divisions,  according  to  the  amount  of 
traffic  they  receive,  i.e.,  those  which  carry  light  traffic,  and 
those  which  carry  heavy  traffic.  In  either  case  the  automobile 
must  be  taken  into  account  and  the  road  treated  accordingly. 
The  surface  application  of  a  semipermanent  binder  in  moder- 
ate quantity  will  usually  prevent  dust  formation  quite  satisfac- 
torily upon  roads  which  are  not  subjected  to  an  excessive 
amount  of  traffic,  but  the  same  will  not  necessarily  hold 
good  for  heavily  traveled  roads.  Here,  as  in  all  cases,  cost 
will  prove  a  most  important  factor.  When  the  first  expense 
can  be  met,  a  well-constructed  bituminous  macadam  will  often 
prove  the  most  economical  in  the  long  run,  but  even  then  the 
application  of  temporary  binders  may  be  required  to  lay  the 
dust  if  much  is  carried  upon  the  road  from  outside  sources. 
As  the  conditions  governing  the  selection  of  permanent  binders 
have  already  been  mentioned  under  country  roads,  it  is  only 
necessary  here  to  consider  those  conditions  influencing  the 
selection  of  temporary  binders,  should  a  choice  in  their  favor 
be  made  over  the  permanent  binders. 

If  a  system  of  hydrants  be  located  at  convenient  distances 
along  the  road,  salt  solutions,  emulsions,  or  waste  sulphite  liquors 
can  be  easily  employed ;  if  not,  recourse  must  be  had  to  one  of  the 
lighter  oil  or  tar  products.  In  the  latter  case  that  product 
which  contains  the  greatest  amount  of  binding  base  per  unit 
cost  should  be  selected  unless  it  possesses  other  qualities  which 
are  particularly  undesirable,  such  as  a  strong  and  disagreeable 
odor.  If  an  emulsion  or  salt  solution  can  be  employed,  the 
character  of  the  road  material  may  determine  which  is  the  more 


392  DUST  PREVENTIVES  AND   ROAD   BINDERS 

suitable.  Thus  a  hard  road,  on  which  the  products  of  wear 
will  be  slight  provided  they  are  retained  upon  the  surface,  or 
one  in  which  the  cementing  value  of  the  rock  dust  is  good,  can 
be  effectively  treated  with  a  solution  of  some  salt  such  as  cal- 
cium chloride.  Also  in  cases  where  the  climate  is  more  or  less 
humid  a  deliquescent  salt  may  give  the  most  satisfactory 
results.  When  the  climate  is  very  arid,  however,  the  salt  will 
have  to  be  fed  with  too  many  applications  of  water  to  make  its 
use  economical.  In  the  case  of  a  road  built  of  very  soft  rock 
which  wears  badly  under  traffic,  the  asphaltic  oil  emulsions  are 
to  be  preferred  on  account  of  the  binding  and  road  building 
qualities  which  they  possess.  As  a  general  rule,  when  it  is 
particularly  desirable  to  obtain  a  road  building  emulsion,  one 
containing  a  volatile  saponifying  agent  might  be  selected  in 
preference  to  the  non-volatile  saponifiers,  especially  in  the  case 
of  an  asphaltic  oil  product  where  the  binding  base  is  apt  to  be 
permanently  injured  by  the  presence  of  fixed  alkalies.  The 
choice  of  other  emulsions  and  light  preparations  will  in  many 
cases  depend  upon  locality.  Where  waste  products  of  a  deliques- 
cent or  binding  character  can  be  obtained,  they  may  be  utilized 
for  the  purpose  of  dust  laying  and  are  apt  to  be  cheaper  than  any 
other  material  in  localities  near  which  they  are  produced. 

Selection  of  Dust  Preventives  for  Use  in  Towns  and  Cities.  - 
In  cities  and  towns  where  the  traffic  is  heavy  and  of  a  mixed 
character,  true  paving  materials  should  undoubtedly  be  selected 
for  construction  work,  but  unless  their  use  is  supplemented  by 
that  of  the  surface  application  of  temporary  binders  dust  pre- 
vention is  almost  an  impossibility.  This  is  to  a  great  extent  due 
to  the  fact  that  large  quantities  of  dust  from  outside  sources  are 
brought  upon  the  streets,  which  makes  it  necessary  to  apply  the 
dust  preventives  at  frequent  intervals.  As  the  semipermanent 
liquid  binders  in  concentrated  form  cannot  be  applied  in  this 
manner  for  obvious  reasons,  recourse  must  be  had  to  the  tem- 
porary binders  or  dust  palliatives. 

In  the  class  of  pavement  having  a  smooth,  unbroken  and 
resilient  surface,  such  as  sheet  asphalt,  conditions  more  closely 


SELECTION  OF  DUST  PREVENTIVES  AND   ROAD  BINDERS       393 

approach  the  ideal  dustless  pavement  than  any  other  so  far 
devised.  The  products  of  wear  are  comparatively  small  in 
quantity  and  there  are  few  cracks  or  crevices  where  dust  can 
accumulate,  and  yet  they  are  by  no  means  dustless,  —  unless 
kept  free  from  dirt  and  refuse  by  frequent  cleanings.  As  this 
type  of  pavement  is  practically  impervious,  no  great  amount  of 
dust  preventive  will  be  absorbed  if  any  is  used  and  most  of  it 
will  be  removed  when  the  street  is  cleaned  unless  it  has  already 
volatilized.  Any  non- volatile  dust  layer  is  apt  to  make  the  pave- 
ment slippery,  and  volatile  materials  evaporate  so  rapidly  in 
hot  weather  that  except  for  laying  the  dust  just  previous  to 
sweeping  they  are  of  little  value.  Water  is  about  the  only 
material  that  seems  to  be  suitable  for  this  class  of  pavements. 

Brick  pavements,  stone  block  pavements  and,  in  fact,  any 
pavements  which  present  a  less  sheet-like  surface  than  the 
asphalt  type  can  be  more  satisfactorily  treated  for  dust  preven- 
tion. On  these  pavements  dust  tends  to  accumulate  in  the 
crevices  between  the  bricks  or  blocks  and  in  moderate  quan- 
tities is  almost  unnoticeable  until  raised  by  winds  or  traffic. 
An  apparently  clean  street  will,  therefore,  often  prove  to  be  a 
very  dusty  one.  The  use  of  a  temporary  binder  to  saturate  this 
dust  and  hold  it  down  until  cleaning  becomes  necessary  can  be 
managed  economically,  as  any  dust  preventive  that  is  applied 
will  have  a  natural  tendency  to  collect  in  just  those  portions  of 
the  road  where  the  dust  has  accumulated  and  if  used  in  moderate 
quantity  should  not  produce  the  undesirable  conditions  result- 
ing from  similar  applications  upon  an  asphalt  pavement.  Solu- 
tions of  calcium  chloride  should  prove  satisfactory  for  this  work, 
but  the  best  form  of  temporary  binder  for  any  particular  pave- 
ment will  in  most  cases  have  to  be  determined  by  experiment. 

Selection  of  Materials  for  Treating  Park  Roads.  —  Before 
leaving  the  subject  of  selection,  a  few  words  may  not  be  amiss 
in  relation  to  city  park  roads.  Here  under  ordinary  circum- 
stances conditions  are  somewhat  different  from  those  pertaining 
to  any  of  the  three  classes  so  far  considered.  In  the  first  place 
park  roads  are  almost  entirely  given  over  to  pleasure  traffic. 


394  DUST  PREVENTIVES  AND   ROAD   BINDERS 

As  they  are  subjected  to  little  or  no  heavy  teaming,  they  are 
usually  of  lighter  construction  than  the  ordinary  road  and  in 
many  cases  are  composed  of  rather  soft  material.  Motor 
traffic  is  likely  to  be  excessive  and  some  suitable  dust  preventive 
is  often  needed. 

Semipermanent  binders  may  be  used  to  advantage  in  many 
cases,  but  as  a*  general  rule  more  economical  and  satisfactory 
results  can  be  obtained  with  temporary  binders.  Soap  solutions 
or  emulsions  of  asphaltic  or  semiasphaltic  oils  have  given  good 
results  at  small  expense  in  a  number  of  instances  where  emulsi- 
fying plants  have  been  established  in  or  near  the  park.  Other 
forms  of  emulsions  as  well  as  salt  solutions  have  also  proved 
effective,  but  usually  at  a  somewhat  greater  cost.  When  soap 
emulsions  of  oil  are  employed,  it  is  necessary  to  give  the  road 
more  attention  than  when  heavier  binding  emulsions  are  used, 
especially  in  cases  where  considerable  loose  material  occurs 
upon  the  road.  The  reason  for  this  has  already  been  considered 
and  it  is  only  necessary  to  add  that  it  does  not  constitute  a 
serious  objection  when  applied  to  park  roads,  as  facilities  are 
usually  such  that  the  work  can  easily  be  handled.  A  choice 
between  permanent,  semipermanent  and  temporary  binders  for 
use  on  park  roads  may  depend  upon  any  one  or  more  of  the 
conditions  already  mentioned  for  the  various  other  classes  of 
roads,  but  in  particular  where  dust  from  outside  sources  is 
likely  to  be  carried  upon  the  road  in  considerable  quantity,  the 
temporary  binders  are  to  be  preferred  to  the  semipermanent. 

Specifications  for  Road  Binders.  —  The  author  has  been 
repeatedly  asked  to  furnish  specifications  for  road  binders,  the 
prevailing  idea  among  road  engineers  seeming  to  be  that  a 
standard  set  of  specifications  should  be  formulated  which  would 
always  insure  satisfactory  results.  To  those  who  have  read  this 
book  it  must  appear  evident  that  this  is  practically  an  impossi- 
bility. No  one  set  of  specifications  of  any  value  can  ever  be 
made  to  cover  all  varieties  of  road  binders.  Even  for  a  single 
type  the  factors  which  control  selection  must  of  necessity  control 
specifications  and  it  has  been  shown  that  these  factors  are 


SELECTION  OF  DUST  PREVENTIVES  AND   ROAD  BINDERS       395 

exceedingly  variable.  Such  considerations  will  always  make  the 
framing  of  specifications  a  matter  of  expert  opinion  for  individual 
cases. 

Where  the  desired  method  of  application,  character  of  the 
road,  and  local  conditions  to  which  it  is  subjected  are  known, 
a  working  basis  is  established  for  the  formulation  of  specifications 
for  a  given  type  of  binder.  If  any  one  of  these  three  factors 
is  unknown,,  however,  there  can  be  no  guarantee  that  a  satis- 
factory material  will  be  furnished  under  specifications. 

Owing  to  the  fact  that  standard  methods  of  examination  have 
not  been  generally  adopted,  it  is  at  present  advisable  to  describe 
the  desired  methods  in  any  set  of  specifications  which  may  be 
framed,  as  otherwise  they  may  become  a  matter  of  controversy. 
The  following  specifications'  will  perhaps  serve  as  a  general 
guide  or  form  for  both  tar  and  oil  products  which  are  to  be 
used  for  specific  purposes.  It  should  be  understood,  however, 
that  the  values  assigned  are  subject  to  change  to  meet  local 
conditions. 

The  tar  specifications  given  below  are  framed  to  secure  a 
suitable  product  for  use  according  to  the  penetration  method  in 
a  southern  locality.  This  product  may  be  prepared  by  the 
distillation  of  either  a  water  gas  tar,  a  low  or  medium  carbon  coal 
tar  or  a  properly  controlled  mixture  of  water  gas  tar  and  coal 
tar.  The  methods  of  examination  required  to  determine  the 
specified  qualities  are  described  in  Chapter  XIII. 

SPECIFICATIONS  FOR  ROAD  TAR. 

TO  BE  USED  ACCORDING  TO  THE  PENETRATION  METHOD  IN  THE 
CONSTRUCTION  OF  TAR  MACADAM  ROADS  IN COUNTY, 

STATE    OF 

(1)  The  tar  shall  have  a  specific  gravity  of  not  less  than 
1.170  nor  greater  than  1.250  at  25°  C. 

(2)  It  shall  be  soluble  in  c.p.  carbon  bisulphide  at  air  tem- 
perature to  at  least  80  per  cent  and  shall  contain  not  over 
20  per  cent  free  carbon,  preferably  much  less. 


396  DUST  PREVENTIVES  AND   ROAD  BINDERS 

(3)  Upon  ignition  it  shall  show  not  over  0.5  per  cent  inor- 
ganic residue. 

(4)  When  a  sample  of  the  tar  is  subjected  to  the  float  test, 
the  float  shall  sink  in  water  maintained  at  50°  C.  in  not  less 
than  two  and  one-half  minutes  nor  more  than  three  minutes. 

(5)  When  250  cc.  of  the  tar  is  distilled  in  a  750  cc.  glass 
retort  at  a  rate  not  exceeding  two  drops  of  distillate  per  min- 
ute, the  total  distillate  to  170°  C.  as  registered  by  a  thermom- 
eter whose  bulb  is  level  with  the  bottom  juncture  of  stem  and 
body  of  the  retort  shall  not  exceed  2  per  cent  by  volume  of  the 
original  material.     The  total  distillate  to  270°  C.  shall  in  no 
case  exceed  50  per  cent,  and  when  the  tar  contains  more  than 
10  per  cent  free  carbon,  this  distillate  shall  not  exceed  40  per 
cent  by  volume  of  the  original  material. 

(6)  The  tar  shall  be  free  from  water  upon  delivery. 

It  may  be  noted  with  reference  to  the  individual  clauses 
that. 

(1)  The  lower  limit  for  specific  gravity  together  with  clause  (3) 
insures  a  tar  product,  and  to  a  certain  extent  controls  the  con- 
sistency of  a  very  low  carbon  tar.     The  higher  limit  controls 
the  consistency  of  a  tar  containing  the  maximum  free  carbon 
contents,  and  together  with  clause  (4)  reinforces  clause  (2). 

(2)  This  clause  is  worded  so  as  to  control  the  free  carbon 
contents  as  determined  according  to  any  method,  and  specif- 
ically by  its  solubility  in  carbon  bisulphide. 

(3)  The  relation  of  this  clause  to  clause  (i)  has  been  de- 
scribed.    It  further  prevents  the  adulteration  of  the  tar  with 
any  inert  mineral  matter. 

(4)  Compliance  with  the  float  test  insures  the  desired  con- 
sistency within  comparatively  narrow  limits  for  tars  of  differ- 
ent free  carbon  contents  and  very  definitely  for  duplicate  lots 
of  tars  containing  the  same  percentage  of  free  carbon. 

(5)  This  clause  insures  what  is  considered  to  be  a  normal 
relation  between  distillates,  both  volatile  and  non-volatile,  and 
residue,  for  tars  which  contain  a  relatively  large  amount  of 


SELECTION   OF  DUST  PREVENTIVES  AND   ROAD  BINDERS       397 

naphthalene.  If  the  absence  of  appreciable  quantities  of  naph- 
thalene had  been  specified,  the  allowable  limit  of  total  distillate 
below  270°  C.  might  have  been  somewhat  lower,  without  danger 
of  the  tar  becoming  rapidly  brittle  under  service  conditions. 
This  clause  also  insures  a  refined  product. 

(6)  Absence  of  water  insures  a  refined  product  and  prevents 
carelessness  in  the  preparation  of  the  tar  in  so  far  as  conden- 
sation is  concerned  if  the  distillation  is  carried  on  by  means  of 
steam.  This  specification  also  averts  trouble  due  to  frothing 
when  the  tar  is  heated  during  application. 

An  oil  product 


ERRATUM. 

396,  line  7,  the  word  "minute 


Page 
should  read  "sceond. 


(4)  When  tested  for  5   seconds  at   25°  C.   with  a  standard 
No.  2  needle  weighted  with  100  grams,  it  shall  show  a  pene- 
tration of  not  less  than  15.0  mm.,  nor  greater  than  25.0  mm.  unless 
the  residue  obtained  from  the  volatilization  test  (see  clause  5) 
shows  a  penetration  of  not  over  20.0  mm.  when  tested  in  the 
manner  above  described. 

(5)  When  20  grams  of  the  material  is  heated  for  5  hours  in  a 
cylindrical  tin  dish  approximately  two  and  one-half  inches  in 
diameter  by  one  inch  high  at  a  constant  temperature  of  163°  C., 


396  DUST  PREVENTIVES  AND   ROAD  BINDERS 

(3)  Upon  ignition  it  shall  show  not  over  0.5  per  cent  inor- 
ganic residue. 

(4)  When  a  sample  of  the  tar  is  subjected  to  the  float  test, 
the  float  shall  sink  in  water  maintained  at  50°  C.  in  not  less 
than  two  and  one-half  minutes  nor  more  than  three  minutes. 

(5)  When  250  cc.  of  the  tar  is  distilled  in  a  750  cc.  glass 
retort  at  a  rate  not  exceeding  two  drops  of  distillate  per  min- 
ute, the  total  distillate  to  170°  C.  as  registered  by  a  thermom- 
eter whose  bulb  is  level  with  the  bottom  juncture  of  stem  and 
body  of  the  retort  shall  not  exceed  2  per  cent  by  volume  of  the 
original  material.     The  total  distillate  to  270°  C.  shall  in  no 


scribed.    T!t  further  prevents  the  adulteration  of  the  tar  with 
any  inert  mineral  matter. 

(4)  Compliance  with  the  float  test  insures  the  desired  con- 
sistency within  comparatively  narrow  limits  for  tars  of  differ- 
ent free  carbon  contents  and  very  definitely  for  duplicate  lots 
of  tars  containing  the  same  percentage  of  free  carbon. 

(5)  This  clause  insures  what  is  considered  to  be  a  normal 
relation  between  distillates,  both  volatile  and  non-volatile,  and 
residue,   for  tars  which  contain  a  relatively  large  amount  of 


SELECTION   OF  DUST  PREVENTIVES  AND   ROAD  BINDERS       397 

naphthalene.  If  the  absence  of  appreciable  quantities  of  naph- 
thalene had  been  specified,  the  allowable  limit  of  total  distillate 
below  270°  C.  might  have  been  somewhat  lower,  without  danger 
of  the  tar  becoming  rapidly  brittle  under  service  conditions. 
This  clause  also  insures  a  refined  product. 

(6)  Absence  of  water  insures  a  refined  product  and  prevents 
carelessness  in  the  preparation  of  the  tar  in  so  far  as  conden- 
sation is  concerned  if  the  distillation  is  carried  on  by  means  of 
steam.  This  specification  also  averts  trouble  due  to  frothing 
when  the  tar  is  heated  during  application. 

An  oil  product  to  be  used  under  similar  conditions  according  to 
the  penetration  method  might  be  required  to  show  the  following 
properties : 

SPECIFICATIONS  FOR  ROAD  OIL. 

TO  BE  USED  ACCORDING  TO  THE  PENETRATION  METHOD  IN  THE 
CONSTRUCTION  OF  OIL  MACADAM  ROADS  IN COUNTY, 

STATE    OF    

(1)  The  oil  shall  have  a  specific    gravity  not  greater  than 
1.05   and  not  less  than  0.98  at  25°  C.  unless  the  residue  ob- 
tained from  the  volatilization  test  (see  clause  5)  has  a  specific 
gravity  of  not  less  than  .985. 

(2)  It  shall  be  soluble  in  c.p.  carbon  bisulphide  at  air  tem- 
perature to  at  least  99  per  cent  and  shall  contain  not  over  0.3 
per  cent  organic  matter  insoluble. 

(3)  It  shall  contain  not  less  than  12  per  cent  nor  more  than 
25  per  cent  of  bitumen  insoluble  in  86°  B.  paraffin  naphtha  at 
air  temperature. 

(4)  When  tested  for  5   seconds  at  25°  C.   with  a  standard 
No.  2  needle  weighted  with  100  grams,  it  shall  show  a  pene- 
tration of  not  less  than  15.0  mm.,  nor  greater  than  25.0  mm.  unless 
the  residue  obtained  from  the  volatilization  test  (see  clause  5) 
shows  a  penetration  of  not  over  20.0  mm.  when  tested  in  the 
manner  above  described. 

(5)  When  20  grams  of  the  material  is  heated  for  5  hours  in  a 
cylindrical  tin  dish  approximately  two  and  one-half  inches   in 
diameter  by  one  inch  high  at  a  constant  temperature  of  163°  C., 


398  DUST  PREVENTIVES  AND  ROAD  BINDERS 

the  loss  in  weight  by  volatilization  shall  not  exceed  20  per 
cent.  The  residue  remaining  shall  show  a  penetration  of  not 
less  than  10.0  mm.  nor  greater  than  20.0  mm.  when  tested  in  the 
manner  hereinbefore  described. 

(6)  Its  fixed  carbon  shall  not  be  less  than  6  per  cent  nor 
greater  than  20  per  cent. 

(7)  The  oil  shall  be  free  from  water  upon  delivery. 

With  reference  to  these  clauses  it  may  be  said  that: 

(1)  The  specific  gravity  limits,  together  with  clause  (2)  elim- 
inate all  of  the  very  fluid  oils,  at  the  same  time  making  al- 
lowance for  cut-back  products  whose  specific  gravities  may  be 
low,  owing  to  the  presence  of  light  volatile  fluxes.     The  upper 
limit  eliminates  tar  products  but  also  the  presence  of  some  of 
the  solid  native  bitumens.     If  it  is  desired  to  include  the  latter 
class  of  materials,  the  clause  should  be  made  to  apply  only  to 
the  bitumen  free  from  mineral  matter. 

(2)  This  clause  insures  a  very  pure  bitumen  practically  free 
from  mineral  matter.     If  it  is  desired  to  include  products  pre- 
pared from  such  materials  as  Trinidad  asphalt,  allowance  should 
be  made  for  considerable  quantities  of  mineral  matter  and  a 
larger  amount  of  insoluble  inorganic  matter.     The  specification 
would  then,  however,  include  oil  products  which  might  be  adul- 
terated with  inorganic  material. 

(3)  This  clause   aims  to  secure  a  certain  degree  of  stability 
in  the  material,  due  to  the  presence  of  asphaltic  hydrocarbons. 
The  highest  limit  provides  against  excessive  blowing  in  the  proc- 
ess of   manufacture  and  to  some   extent   against  a  tendency 
toward  extreme  lack  of  ductility. 

(4)  The   penetration   specification   provides   for   the   proper 
consistency  both  of   residual  and  cut-back   products,  for   the 
particular  class  of  work  under  consideration. 

(5)  This  clause  reinforces  clause   (4)   and  insures  that  the 
material  will  attain  but  not  exceed  the  necessary  degree  of 
hardness  under  service  conditions.     At  the  same  time  it  provides 
against  excessive  loss  by  volatilization. 


SELECTION   OF   DUST   PREVENTIVES   AND   ROAD   BINDERS      399 

(6)  This  clause  reinforces  clause  (3)  and  eliminates  the  truly 
paraffin  materials. 

(7)  This  clause  prevents  frothing  when  the  material  is  heated. 
Summary  and  Conclusions.  —  In  this  chapter  the  author  has 

attempted  by  a  general  discussion  of  the  subject  of  selection  and 
the  consideration  of  a  few  specific  cases  to  develop  the  principles 
which  should  govern  the  selection  and  specification  of  dust 
preventives  and  road  binders.  It  has  been  possible  to  do  this 
in  only  a  very  limited  way,  owing  to  the  great  number  of  factors 
which  may  modify  selection.  Local  conditions  to  which  a  road  is 
subjected  have  been  shown  to  comprise  some  of  the  most  im- 
portant of  these  factors  but  the  primary  purpose  for  which  any 
material  is  employed  should  never  be  lost  sight  of.  Thus  for 
dust  prevention  only  a  temporary  binder  or  palliative  may  be 
employed,  but  never  with  the  expectation  that  it  will  serve  as  a 
permanent  binder.  On  the  other  hand,  the  permanent  binders, 
while  of  great  value  as  dust  preventives  so  far  as  the  wear  of 
the  road  is  concerned,  cannot  be  expected  to  serve  indefi- 
nitely as  dust  layers.  Other  considerations  which  may  govern 
selection  are  cost,  ease  of  application,  imperviousness,  time 
required  before  traffic  can  be  admitted  to  the  road  after  treat- 
ment, freedom  from  harmful  and  offensive  qualities,  slipperiness, 
etc.  It  should  be  remembered,  however,  that,  no  matter  how 
much  care  and  attention  is  paid  to  selection,  unless  the  material 
is  properly  applied  and  the  road  in  proper  shape  to  be  treated, 
satisfactory  results  will  not  be  obtained.  Moreover,  the  necessity 
for  careful  and  constant  maintenance  should  never  be  forgotten 
if  the  work  is  to  be  put  upon  the  most  economical  basis  possible. 
Such  aids  to  dust  prevention  and  road  preservation  as  men- 
tioned in  Chapter  I  will  also  be  found  serviceable  in  cases  where 
they  can  be  utilized. 


APPENDIX 


COMPARISON    OF   DEGREES    BAUME"    AND    SPECIFIC    GRAVITY. 

(Liquids  lighter  than  water.) 


(1)  Sp.gr.  = 

(2)  °B  = 


140 


130  +  °Be 
140 


at  i7.5°C 


Sp.  gr. 


-  130  at  i7-5°C. 


°Be. 

Sp.  Gr. 

°Be. 

Sp.  Gr. 

IO 

I  .  0000 

46 

°-7954 

ii 

.9929 

47 

.7909 

12 

•  9859 

48 

.7865 

13 

.9790 

49 

.7821 

14 

.9722 

5° 

•7777 

15 

•9655 

•7734 

16 

•  9589 

52 

.7692 

17 

•9523 

53 

.7650 

18 

•9459 

54 

.7608 

19 

•9395 

55 

•7567 

20 

•9333 

56 

.7526 

21 

.9271 

57 

.7486 

22 

.9210 

58 

.7446 

23 

.9150 

59 

.7407 

24 

.9090 

60 

.7368 

5 

.9032 
.8974 

70 
71 

.7000 
.6965 

11 

.8917 
.8860 

72 
73 

.6931 
.6896 

29 

.8805 

74 

.6863 

3° 

.8750 

75 

.6829 

.8695 

76 

.6796 

32 

.8641 

77 

.6763 

33 

.8588 

78 

.6731 

34 

•8536 

79 

.6698 

35 

.8484 

80 

.6666 

36 

•8433 

81 

•6635 

•8383 

82 

.6604 

38 

8333 

83 

•6573 

39 

.8284 

84 

.6542 

40 

•8235 

85 

.6511 

41 

.8187 

86 

.6482 

42 

•8139 

87 

.6452 

43 

.8092 

88 

.6422 

44 

.8045 

89 

•6393 

45 

.8000 

90 

•6363 

400 


APPENDIX 


401 


COMPARISON  OF  DEGREES  BAUMlS  AND  SPECIFIC  GRAVITY. 

(Liquids  heavier  than  water.) 


(2)         •W-MS-g^.tiS.S'C 


°Be. 

Sp.  Gr. 

°Be. 

Sp.  Gr. 

o 

.0000 

18 

.1417 

I 

.0069 

19 

.1508 

2 

.0140 

2O 

.  1600 

3 

.0211 

21 

.1694 

4 

.0284 

22 

.1789 

5 

•0357 

23 

•1885 

6 

.0432 

24 

.1983 

I 

.0507 
.0584 

25 
26 

.2083 
.2185 

9 

.0662 

27 

.2288 

10 

.0741 

28 

•2393 

ii 

.0821 

29 

.2500 

12 

.0902 

30 

.2609 

13 

.0985 

31 

.2719 

14 

.  1069 

32 

.2832 

15 

•1154 

33 

.2946 

16 

.I24O 

34 

I  .  3063 

17 

.1328 

35 

1.3182 

402 


DUST  PREVENTIVES   AND   ROAD   BINDERS 


COMPARISON  OF  CENTIGRADE   AND  FAHRENHEIT  DEGREES. 

(1)  °F.=  |°C.+  32 

(2)  °C.  -    5(°R~32) 


c. 

F. 

C. 

F. 

C. 

F. 

C. 

F. 

C. 

F. 

C. 

F. 

0 

32- 

38 

100.4 

76 

168.8 

114 

237.2 

152 

305-6 

190 

374. 

i 

33-8 

39 

IO2.2 

77 

170.6 

115 

239- 

153 

307-4 

191 

375-8 

2 

35-6 

40 

104. 

78 

172.4 

116 

240.8 

154 

309.2 

192 

377-6 

3 

37-4 

4i 

105.8 

79 

174.2 

117 

242.6 

!55 

3ii- 

193 

379-4 

4 

39-2 

42 

107.6 

80 

176. 

118 

244.4 

156 

312.8 

194 

381.2 

s 

41. 

43 

109.4 

81 

177.8 

119 

246.  2 

i57 

314.6 

195 

383- 

6 

42.8 

44 

III  .2 

82 

179.6 

120 

248. 

158 

3i6.4 

196 

384.8 

7 

44.6 

45 

113- 

83 

181.4 

121 

249.8 

i59 

318-2 

197 

386.6 

8 

46.4 

46 

II4-8 

84 

183.2 

122 

251.6 

1  60 

320. 

198 

388.4 

9 

48.2 

47 

116.6 

85 

185- 

123 

253-4 

161 

321-8 

199 

390.2 

10 

5°- 

48 

118.4 

86 

186.8 

124 

255-2 

162 

323-6 

200 

392. 

ii 

5i-8 

49 

120.2 

87 

188.6 

I25 

257- 

163 

325-4 

210 

410. 

12 

53-6 

50 

122. 

88 

190.4 

126 

258.8 

164 

327.2 

220 

428. 

J3 

55-4 

5i 

123.8 

89 

192.2 

127 

260.6 

165 

329- 

230 

446. 

14 

57-2 

52 

125.6 

90 

194. 

128 

262.4 

1  66 

330.8 

240 

464. 

15 

59- 

53 

127-5 

9i 

195.8 

I29 

264.2 

167 

332-6 

250 

482. 

16 

60.8 

54 

129.2 

92 

197.6 

130 

266. 

1  68 

334-4 

260 

500. 

J7 

62.6 

55 

I3I- 

93 

199.4 

131 

267.8 

169 

336.2 

270 

5i8. 

18 

64.4 

56 

132.8 

94 

201.2 

132 

269.6 

170 

338. 

280 

536. 

IQ 

66.2 

57 

134.6 

95 

203. 

133 

271.4 

171 

339-8 

290 

554- 

20 

68. 

58 

136.4 

96 

204.8 

134 

273-2 

172 

341.6 

300 

572. 

21 

69.8 

59 

138.2 

97 

206.6 

135 

275- 

173 

343-4 

350 

662. 

22 

71.6 

60 

140. 

98 

208.4 

I36 

276.8 

174 

345-2 

4OO 

752. 

23 

73-4 

61 

I4I.8 

99 

210.2 

137 

278.6 

175 

347- 

45° 

842. 

24 

75-2 

62 

143.6 

100 

212. 

138 

280.4 

176 

348.8 

500 

932. 

25 

77- 

63 

145-4 

101 

213.8 

139 

282.2 

177 

35°-6 

550 

1022. 

26 

78.8 

64 

147.2 

102 

215.6 

140 

284. 

178 

352.4 

600 

III2. 

27 

80.6 

65 

149. 

I03 

217-4 

141 

28^.8 

179 

354-2 

650 

1202. 

28 

82.4 

66 

150.8 

104 

219.2 

142 

287.6 

1  80 

356. 

700 

1292. 

29 

84.2 

67 

152.6 

i°5 

221. 

143 

289.4 

181 

357-8 

75° 

1382. 

3° 

86. 

68 

154.4 

106 

222.8 

144 

291.2 

182 

359-6 

800 

1472. 

31 

87.8 

69 

156.2 

107 

224.6 

145 

293- 

183 

361.4 

850 

1562. 

32 

89.6 

7° 

158. 

1  08 

226.4 

146 

294.8 

184 

363-2 

900 

l652. 

33 

91.4 

71 

159.8 

109 

228.2 

147 

296.6 

185 

365- 

95° 

1742. 

34 

93-2 

72 

161.6 

no 

230. 

148 

298.4 

186 

366.8' 

ooo 

l832. 

35 

95- 

73 

163.4 

in 

231.8 

149 

300  .  2 

187 

368.6 

2OO 

1992. 

36 

96.8 

74 

165.2 

112 

233-6 

150 

302. 

188 

37°-4 

500 

2732. 

37 

98.6 

75 

167. 

H3 

235-4 

I5i 

303-8 

189 

372.2 

ooo  3632  . 

APPENDIX 


403 


10.8 
10.6 
10.4 
10.2 
10.0 
9.8 

9.6 
d 

1  9A 
^9.2 

&9.0 

1 
g  8.8 

£  8.6 
8.4 
8.2 
8.0 
7.8 
7.6 
7.4 
7.2 
7.0 

180 
190 
200 
210  1 

220g 

230^ 

d 

240  H 

260| 
270| 
280 
290 
300 

., 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

^ 

/ 

^ 

^, 

^ 

^ 

/ 

^ 

^ 

x 

7 

^ 

^"^ 

x 

/ 

^X 

^^ 

/ 

^x 

x 

, 

/, 

X 

^ 

" 

X 

> 

X 

X 

7 

/ 

/ 

/ 

.85 


.90 


.95 


1.00         1.05         1.10 
Specific  Gravity 


1.15        1.30 


1.S5 


FIG.  50. 

Diagram  showing  the  number  of  pounds  per  gallon  and  the  number  of  gallons 
per  ton  (2000  Ibs.)  for  liquids  of  known  specific  gravity. 


404 


DUST  PREVENTIVES  AND   ROAD  BINDERS 


26,000 

24,000 

22,000 

20,000 

18,000 

j§  16,000 

w  14,000 

O  12,000 

10,000 

8,000 

6,000 

4,000 

2,000 


1.8 


1.7 


1.6 


10 


14  16 

Width  of  Road  (Feet) 


18 


20 


FIG.  51. 

Diagram  showing  the  number  of  gallons  of  material  required  to  treat  one  mile 
of  roadway  of  known  width,  at  given  rates  of  application  per  square  yard. 


INDEX 


PAGE 

Acenaphthene 128 

Acetylenes 120 

Aggregate,  method  of  sizing 379 

Alkalies,  determination  of,  in  cements 101 

Aloes,  oil  of,  as  a  dust  preventive 104 

Alumina,  determination  of,  in  cements 99 

American  Society  for  Testing  Materials,  methods  of  examining  bituminous 

road  materials,  proposed  by 374 

American  Society  of  Civil  Engineers,  methods  of  examining  bituminous  road 

materials  adopted  by 379 

Amiesite 320 

pavement,  characteristics  of 321 

Animal  fats,  as  dust  preventives  and  road  binders 33,  104 

Anthracene 127 

Anti-skidding  devices,  effect  upon  roads 12: 

Asphalt,  Bermudez 186,  190,  191 

California 191 

Cuban 191,  192: 

cutter 312 

Maracaibo 191 

Mexican 191: 

oil  mixing  plant 313. 

Trinidad 185,  190,  191 

Asphaltic  cements,  blown  oil  gilsonite 195; 

comparison  of,  for  road  and  paving  work 196* 

constituents  of 192 

gilsonite  oil  tar 195; 

preparation  of 193. 

Asphalts,  as  road  binders 35 

native 184 

refining  of 187 

Astatki,  value  of,  for  road  treatment 200 

Automobiles,  effect  of,  upon  roads 8- 

production  of,  in  the  United  States 23, 

Benzene  series  of  hydrocarbons 124 

Bichromate  of  potash,  use  of,  in  road  preparations 104 

Binders,  classification  according  to  chemical  characteristics 32 

use 27 

405 


406  INDEX 

PAGE 

Binders,  methods  of  applying 19 

necessity  for  information  concerning 20 

permanent 31 

semipermanent 29 

temporary > • 28 

Bittern,  as  a  dust  preventive 43 

Bitumen,  definition  of ; 131 

soluble  in  carbon  disulphide,  method  of  determination  proposed  by 

Am.  Soc.  Test.  Mat 374,  376 

Bitumens  artificial 134 

preparation  of 135 

comparison  of  solid  native 189 

native,  as  dust  preventives  and  road  binders 34 

definition  of .  .  .'. 132 

origin   of 133 

pyro- 136 

Bituminized  aggregates,  examination  of 370 

patent  and  proprietary 318 

Bituminous  concrete,  cost  of  hand  mixing 308 

hand  mixing  plant  for ;  .  .  .  .  304 

mechanical  mixing  of 309 

macadam,  characteristics  of.  ..." 315 

aggregate  for 317 

construction  of,  mixing  method 300 

penetration  method 293 

Glad  well  method  of  constructing 314 

hand  mixing  for 303 

mechanical  mixing  for 309 

method  of  repairing ' 317 

resurfacing,  mixing  method 303 

penetration  method 300 

sand-filled,  construction  of 299 

materials,  classification  of 137 

examination  of  general  characteristics 327 

factors  governing  examination  of .  , 326 

methods  of  examination  adopted  by  Am.  Soc.  Civ.  Eng.  79 
methods  of  examination  proposed  by  Am.  Soc.  Test. 

Mat 374 

road  materials,  value  of  examination  of .' 325 

rock,  production  of,  in  the  United  States 180 

Blowing  oils,  effect  of 362 

Blown  oils 158,  160,  172 

Burning  point  determination,  value  of 336 

of  oils,  method  of  determining 335 

Calcium' chloride,  application  of 47 

as  a  dust  preventive 33,  43 


INDEX  407 

PAGE 

Calcium  chloride,  as  a  dust  preventive,  advantages  and  disadvantages 51 

cost  of 46 

examination  of 53 

hygrocopicity  as  compared  with  magnesium  chloride 44 

manufacture  of 45 

properties  of 43 

solutions,  specific  gravity  of 48 

determination  of,  in  calcium  chloride 53 

Camphene 128 

Carbenes 363 

Carbon  atom 112 

tetrachloride  insoluble  bitumen,  determination  of 363 

Am.  Soc.  Civ.  Eng.  382 

Cement  concrete,  proportion  of  ingredients  of So- 
testing,  methods  of 83 

Cementation  index  of  cements,  method  of  determining 73 

Cementing  value  of  rock  powders,  method  of  determining 64 

Cements,  analysis  of 97 

as  road  binders 33 

hydraulic,  properties  of 72 

natural,  manufacture  and  properties  of 74 

specifications  for 74 

Portland,  manufacture  and  properties  of 75 

specifications  for 76 

puzzolan  (see  slag  cement) 77 

slag,  manufacture  and  properties  of 77 

specifications  for 78 

use  of,  in  road  construction 79 

Chlorine,  determination  of,  in  calcium  chloride 55 

Cities,  selection  of  dust  preventives  for  use  in 392: 

Classification  of  bituminous  materials 137 

dust  preventives  and  road  binders  (tabular) 36 

Cleveland  oil  tester 335 

Coal  tar  (see  tar). 

theory  of  formation  of 242 

Coke  oven  tar  (see  tar). 

Coke  ovens,  beehive 239 

by  product 239 

Consistency  determination  for  bitumens,  Am.  Soc.  Test.  Mat 377 

normal,  method  of  determining,  for  cement  mortars 88 

Vicat  needle  apparatus  for  determining 88 

Cottonseed  oil,  use  of,  in  road  preparations 104 

Country  roads,  selection  of  materials  for  treating 386 

Crempoid 104 

Determination  of  alkalies  in  cement 101 

alumina  in  cement 99 


408  INDEX 

PAGE 

Determination  of  bitumen  insoluble  in  carbon  tetrachloride .  > 363,  382 

naphtha 360,  383 

soluble  in  carbon  bisulphide 356,  374,  376 

burning  point  of  oils -. 335 

calcium  in  calcium  chloride 53 

cementing  value  of  rock  powders 64 

chlorine  in  calcium  chloride 55 

ductility  of  bitumens 348 

fineness  of  cement 87 

fixed  carbon  in  oils 363,  378,  380 

flash  point  of  oils 335 

free  carbon  in  bitumens 360,  379 

iron  in  cements 99 

lime  in  cements 100 

magnesia  in  cements 100 

magnesium  in  calcium  chloride 54 

melting  point  of  bitumens 349,  381 

normal  consistency  of  cement  mortars 88 

paraffin  scale 364,  382 

setting  time  of  cement 90 

silica  in  cement 98 

size  particles  in  aggregates 379 

slaking  value  of  rock  powders 68 

sodium  in  calcium  chloride 54 

specific  gravity  of  bitumens 328 

cement 84 

sulphur  in  cement 101 

sulphuric  anhydride  in  cement 101 

tensile  strength  of  cement 92 

total  bitumen 356 

water-soluble  materials  in  bitumens 379,  382 

viscosity  of  bitumens .  .  : 337 

Distillation  test  of  tars 366,  381 

value  of ' 369 

Dow  Penetration  Machine 342 

Ductility  test  of  bitumens .     348 

Dust,  causes  of  formation  of,  upon  roads 4 

effect  upon  animal  life 3 

plant  life 3 

formation,  chemical  agencies  of 5 

mechanical,  agencies  of 6 

physical,  agencies  of 6 

prevention,  methods  of 13 

preventives,  classification  according  to  chemical  characteristics 32 

use 27 

factors  governing  selection  of 384 

necessity  for  information  concerning 20 


INDEX  409 

PAGE 

Dust  preventives,  permanent 31 

semipermanent 29 

temporary .' . .  .  28 

problem 2 

relation  to  road  preservation 7 

transportation  of  germs  by  means  of 3 

Earth  roads,  construction  of,  with  oil 214 

oiled,  future  of 220 

surface  treatment  of,  with  oils 209 

Emulsifying  road  oils,  preparation  of 175 

properties  of 175 

Emulsions,  application  of 49 

Engler's  viscosimeter 337 

Evaporation  test  of  tars,  Am.  Soc.  Civ.  Eng 380 

Examination  of  bituminized  aggregates 370 

bituminous  materials,  factors  governing 326 

calcium  chloride 53 

Fineness,  method  of  determining,  of  cements 87 

Fitzsimmons  patent  dust  layer 56 

Fixed  carbon  determination 363 

Am.  Soc.  Civ.  Eng 380,  382 

value  of 364 

or  residual  coke  determination,  Am.  Soc.  Test.  Mat 378 

Flash-point  determination,  value  of 336 

of  oils,  method  of  determining 335 

Float  test  for  bituminous  materials 339 

value  of 341 

Fluorene 128 

Fluxing  plant 313 

Free  carbon  determination,  Am.  Soc.  Civ.  Eng 379,  382 

determination  of,  in  bitumens 360 

effect  of,  in  tars 251,  264 

Future  road 22 

Gas-house  tar  (see  tar). 

Gilsonite 188,  190,  191 

Glad  well  method  of  constructing  bituminous  macadam 314 

Glue,  use  of,  in  road  preparations 104 

Glutrin 106 

Grahamite 189,  190,  191 

Gravel  roads,  construction  of,  with  oils , *  221 

surface  treatment  of,  with  oils 210 

Hand  mixing  for  bituminous  macadam 303 

Harrow,  spike  disc 218 


410  INDEX 

PAGE 

Hassam  pavement 82 

Hydraulic  cements,  properties  of 72 

Hydrocarbon  radicals 115 

Hydrocarbons,  acenaphthene  series 1 28 

acetylenes 1 20 

anthracene  series 127 

benzene  series 124 

camphan  group 128 

coal  tar,  theory  of  formation  of 242 

cyclic,  saturated 121 

unsaturated 123 

derivatives 129 

fluorene  group 128 

found  in  bituminous  road  materials,  table  of 130 

indene  group 127 

isomers  of 116 

naphthalene  series 1 26 

naphthenes 121 

defines 1 18 

open  chain,  saturated 114 

unsaturated 118 

paraffins 114 

polyphenyls 125 

Impact  Machine,  Page 67 

Indene 127 

Inorganic  dust  preventives  and  road  binders 32 

Iron,  determination  of,  in  cements 99 

Lime,  determination  of,  in  cements 100 

effect  upon  cementing  value  of  rock  dust 62 

Limewater,  effect  upon  cementing  value  of  rock  dust 62 

Linseed  oil,  use  of,  in  road  preparations 104 

Lymenite 57 

Macadam,  oil-asphalt,  construction  of 223 

roads,  surface  treatment  of,  with  oils 211 

use  of  large  stones  in  wearing  surface  of 18 

rock  asphalt,  construction  of 225 

Magnesia,  determination  of,  in  cements 100 

Magnesium  chloride,  as   a  dust  preventive 33 

effect  of,  in  sea  water 42 

•                        hygroscopicity  as  compared  with  calcium  chloride ....  44 

determination  of,  in  calcium  chloride 54 

Maintenance,  necessity  for 18 

Maltha,  California,  properties  of 179 

formation  of 178 


INDEX 

Maltha,  production  of,  in  the  United  States 179 

Masut,  value  of,  for  road  treatment 200 

Melting  point  determination,  Am.  Soc.  Civ.  Eng 381,  382,  383 

value  of 350 

of  bitumens,  determination  of 349 

Mixing  method  of  constructing  bituminous  macadam 300 

Molasses  as  a  dust  preventive  and  road  binder 34,  109 

oil  lime  mixture,  experiment  with 109 

Motor  dust  trials 15 

vans,  effect  upon  roads 24 

Naphtha  insoluble  bitumen  determination,  Am.  Soc.  Civ.  Eng 383 

determination  of 360 

value  of 361 

Naphthalene 1 26,  268 

Naphthenes 121 

Natural  cement 74 

New  York  Testing  Laboratory  float  apparatus 340 

penetrometer 346 

Oil  (see  petroleum). 

asphalts,  production  of,  in  1908 171 

heating  truck 295 

of  aloes 104 

sprinklers 205 

sprinklers,  American  Tar  Co.'s 207 

Asphaltoilene 206 

Saybolt's 205 

tar  (see  tar). 

Oiled  roads,  cost  of 227 

Oils,  effect  of,  upon  soils 209,  219 

measurement  of  hot 208 

quantity  required  to  treat  macadam  road  surfaces 212 

specifications  for 397 

Olefines 118 

Organic  non-bituminous  dust  preventives  and  road  binders 33 

Page  Impact  Machine 67 

Paraffin  scale,  determination  of 364 

value  of 365 

Paraffin  determination,  Am.  Soc.  Civ.  Eng 382 

Paraffins,  properties  of 117 

Park  roads,  selection  of  materials  for  treating 393 

Penetration  method,  advantages  and  disadvantages  of 297 

of  constructing  bituminous  macadam 293 

test  for  bitumens 341 

Penetrometer,  Dow's 342 

New  York  Testing  Laboratory 346 


412  INDEX 


PAGE 


Petroleum  acid  sludge 160 

Appalachian  field,  characteristics  of 146 

asphaltic  residuum 167 

blown,  products 158 

residuum,  properties  of 160,  172 

California  field,  characteristics  of 151 

residuum,  properties  of ; 152 

Colorado 153 

cracking 157 

crude 161 

asphaltic 162 

California 163 

paraffin 162 

semiasphaltic » 162 

cut-back  products 165 

distillates 163 

early  experiments  with,  in  road  treatment 198 

emulsions 173 

application  of 201 

cost  of  applying 201 

preparation  of 176 

properties  of 175 

fields  in  the  United  States 145 

fluid  residuums 166 

road  oil  residuums,  properties  of 169 

general  application  of 199 

gulf  field,  characteristics  of 151 

residuum,  properties  of 151 

Illinois  field,  characteristics  of 149 

residuum,  properties  of 150 

Kansas  residuum,  properties  of 150 

Lima-Indiana  field,  characteristics  of 148 

measurement  of  hot 208 

Mid-continent  field,  characteristics  of 150 

occurrence  of 153 

Ohio-Indiana  field,  characteristics  of 148 

Ohio  residuum,  properties  of 149 

paraffin  residuum 167 

Pennsylvania  residuum,  properties  of 147 

production  of,  by  fields 146 

in  the  United  States 143 

refining,  preliminary 155 

residual  pitch,  properties  of 172 

residuums,  preparation  of 156 

semiasphaltic 167 

semisolid  and  solid 170 

solid,  properties  of 172 


INDEX 


413 


PAGE 

Petroleum  stills 154 

surface  application  of  crude 200 

heavy  crude  and  refined 204 

Wyoming 152 

Petroleums  and  their  products,  as  dust  preventives  and  road  binders 34 

Petrolithic  earth  road,  construction  of 217 

macadam,  construction  of 222 

Polyphenyls 125 

Potassium  silicate,  as  a  dust  preventive  and  road  binder 57 

Portland  cement 75 

Preservation  of  roads,  methods  of 13 

Pyrobitumens 136 

Quantities  of  material  required  to  treat  one  mile  of  roadway  at  different  rates 

of  application 405 

Quarrite 319 

Resinates  as  road  binders 34,  in 

Road  Congress,  First  International,  purpose  of i 

Road  preservation,  methods  of 13 

Road,  the  future 22 

Road-oil,  specifications  for 397 

Road-tar,  specifications  for 395 

Roads,  oiled,  cost  of 227 

Rock  asphalt,  Kentucky,  properties  of 184 

macadam,  construction  of 226 

occurrence  of,  in  the  United  States 180 

properties  of 182 

use  of,  in  resurfacing  macadam  roads 226 

dust,  as  a  road  binder 58 

effect  of  lime  upon  cementing  value  of 62 

lime  water  upon  cementing  value  of 62 

mixtures  upon  cementing  value  of 61 

water  on 59 

method  of  determining  cementing  value  of 64 

slaking  test  for 68 

Rolling  tamper 215 

Rosin  as  a  road  binder 34,  1 1 1 

oils,  use  of,  in  road  preparations 104 

Sand-filled  bituminous  macadam,  construction  of 299 

Sandisize 104 

Sea  water,  as  a  dust  preventive 42 

Selection  of  dust  preventives  for  use  in  cities 392 

Selection  of  materials  for  treating  country  roads 386 

park  roads 393 


414  INDEX 

PAGE 

Selection  of  materials  for  treating  suburban  roads 391 

Setting  time  of  cements,  method  of  determining 90 

Shale  oils,  value  of,  for  road  treatment 200 

Silica,  determination  of,  in  cement 98 

Slag  cement 77 

dust,  as  a  road  binder 69 

colorimetric  test  for  determining  cementing  value  of 69 

experiments  with 70 

value  of,  in  bituminous  macadam  construction 318 

Slaking  test  of  rock  powders 68 

Sodium,  determination  of,  in  calcium  chloride 54 

Sodium  silicate,  as  a  dust  preventive  and  road  binder 33 ,  56 

manufacture  of 56 

properties  of 57 

Soils,  effect  of,  upon  oils 209,  219 

Solutions,  application  of 49 

Specific  gravity,  Le  Chatelier's,  apparatus 85 

of  bitumens,  hydrometer  determination 328 

methods  of  determining 328 

adopted  by  Am.  Soc. 

Civ.  Eng 379 

pycnometer  determination 328 

Sommer's  method  of  determining 330 

value  of  determination  of 332 

calcium  chloride  solutions 48 

cements,  method  of  determining 84 

liquids  heavier  than  water,  comparison  with  Baume  degrees  401 

lighter  than  water,  comparison  with  Baume  degrees  400 

relation  of,  to  pounds  per  gallon  and  gallons  per  ton  403 

tars,  relation  of,  to  free  carbon  contents 333 

Specifications,  factors  governing 394 

for  natural  cements 74 

Portland  cements 75 

road-oil 397 

road-tar 395 

slag  cements 78 

Spike  disc  harrow 218 

Standard  sand  for  cement  mortars 91 

tests  for  road  materials,  report  of  Am.  Soc.  Test.  Mat 373 

Suburban  roads,  selection  of  materials  for 391 

Sulphite  liquor,  application  of 108 

as  a  dust  preventive  and  road  binder 34,  105 

cementing  value  of 106 

manufacture  of 106 

mixed  with  petroleum 107 

Sulphur,  determination  of,  in  cements 101 

Sulphuric  anhydride,  determination  of,  in  cements 101 


INDEX  415 

PAGE 

Tar,  coal,  rank  of  states  in  production  of 231,  232 

formation  of,  in  the  manufacture  of  coal  gas 234 

coke  oven,  formation  of 240 

Tar  distributors 286 

American 207 

heating  kettle 283 

loss  of,  in  the  United  States 237 

oil  gas 250 

pavement  at  Washington,  D.  C 276 

production  of,  in  the  United  States 229 

quantity  required  to  treat  macadam  road  surfaces 291 

refining 265 

still,  German 266 

water  gas  and  oil  gas,  production  of,  in  the  United  States 233 

manufacture  of , 246 

Tarmac 319 

Tarred  roads,  necessity  for  proper  maintenance  of 290 

Tars  and  tar  products,  as  dust  preventives  and  road  binders 35 

application  of,  to  cement  concrete  surfaces 292 

blown,  properties  of • 272 

coke  oven 239 

crude,  application  of 279 

crude  coal,  characteristics  of 236 

coke  oven,  properties  of 241 

gas  house,  properties  of 237 

water  gas,  properties  of 249 

dehydrated,  properties  of : 269 

distillation  of 267 

early  use  of,  in  road  treatment 275 

effect  of  free  carbon  in 251 

residual,  properties  of 270 

specifications  for .  . 395 

surface  application  of  heavy 280 

light 278 

Tarspra  machine ' 286 

Tar-spraying  machine,  Aitkin's  Pneumatic 287 

Temperatures,  comparison  of  Centigrade  and  Fahrenheit '. 402 

Tensile  strength  of  cements,  method  of  determining 92 

Total  bitumen,  determination  of 356 

value  of 358 

Towns,  selection  of  dust  preventives  for  use  in 392 

Vegetable  oils,  as  dust  preventives  and  road  binders 33,  103 

Viscosimeter,  Engler's 337 

Viscosity  determination,  value  of 339 

of  bitumens,  method  of  determining.  . 337 

methods  adopted  by  Am.  Soc.  Civ.  Eng 381,  383 


416  INDEX 

PAGE 

Voids,  method  of  obtaining  minimum  percentage 303 

Volatilization  test  of  bitumens 352 

Am.  Soc.  Test.  Mat 377 

Volume,  test  for  constancy  of,  in  cements 96 

Warrenite 320 

Water,  application  of 41 

as  a  dust  preventive  and  road  binder 33,  39 

cost  of  applying 41 

effect  of,  upon  rock  powders 40,  59 

Water  gas  tar  (see  tar). 

glass,  properties  of 57 

Water  soluble  materials,  determination  of,  in  bitumens,  Am.  Soc.  Civ.  Eng.    379,  382 
Wool  grease,  as  a  dust  layer 105 


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